A chemical reaction is a process in which reactants are converted into products. Chemical equations are used to illustrate chemical reactions. In a chemical reaction, the conversion of reactants into products results in some observable features known as characteristics of chemical reactions. The important characteristics are the Evolution of a gas, formation of a precipitate, Change in colour, Change in temperature and Change in the state. Anyone of these general characteristics can tell us whether a reaction had taken place or not.
What is a Chemical Reaction?
When two or more molecules combine to produce a new product, it is called a chemical reaction (s). Reactants are chemicals that combine to generate new compounds, whereas products are newly produced compounds.
Chemical reactions are important in a variety of businesses, cultures, and even our daily lives. They are always occurring in our environment, such as rusting of iron, pottery, and wine fermentation, to name a few. A chemical change must occur in a chemical reaction, which is commonly observed with physical changes such as precipitation, heat generation, colour change, and so on.
A reaction can occur between two atoms, ions, or molecules, in which they establish a new link without destroying or creating an atom, yet a new product is generated from reactants. The rate of reaction is influenced by variables such as pressure, temperature, and reactant concentration.
In a chemical reaction, the transformation of reactants into products is frequently accompanied by specific characteristics that may be seen. Chemical reactions have a number of significant properties like:
Evolution of a Gas
Some chemical reactions are characterized by the evolution of gas.
The chemical reaction between sodium sulfite and dilute hydrochloric acid is characterized by the evolution of sulfur dioxide gas.
Na2SO3 + 2HCl ⇢ 2NaCl + H2O + SO2
The chemical reaction between zinc and sulfuric acid is characterized by the evolution of sulfur dioxide hydrogen gas.
Zn + H2SO4 ⇢ ZnSO4 + H2
Formation of a Precipitate
Some chemical reactions are characterized by the formation of a precipitate.
The chemical reaction between copper sulfate and sodium hydroxide is characterized by the formation of a blue precipitate of copper hydroxide.
CuSO4 + 2NaOH ⇢ Na2SO4 + Cu(OH)2
The chemical reaction between silver nitrate and sodium chloride is characterized by the formation of a white precipitate of silver chloride.
AgNO3 + NaCl ⇢ NaNO3 + AgCl
Change in Color
Some chemical reactions are characterized by changes in colour.
The chemical reaction between citric acid and potassium permanganate solution is characterized by a change in colour from purple to colourless. Citric acid oxidizes potassium permanganate because it is a reducing agent.
3KMnO4 + C6H8O7 ⇢ 3HMnO4 + C6H5K3O7
The chemical reaction between sulfur dioxide and acidified potassium dichromate solution is characterized by a change in colour from orange to green.
SO2 + K2Cr2O7 + 3H2SO4 ⇢ K2SO4 +Cr2(SO4)3 + 3H2O
Change in Temperature
The chemical reaction between quicklime and water to form slaked lime is characterized by a change in rising in temperature.
CaO + H2O ⇢ Ca(OH)2
The chemical reaction between barium hydroxide and ammonium chloride to form barium chloride, ammonia and water are characterized by a change in fall in temperature.
BaCl2 + NH4OH ⇢ Ba(OH)2 + NH4Cl
Change in State
Some chemical reactions are characterized by changes in state.
The combustion reaction of candle wax is characterized by a change in state from solid to liquid and gas.
CXHY + O2 ⇢ CO2 + H2O + Heat and Light
Sample Questions
Question 1: State the various characteristics of chemical reactions.
Answer:
The characteristics of a chemical reaction are: Evolution of gas, Formation of a precipitate, Change in colour, Change in temperature, Change in state etc.
Question 2: State two characteristics of the chemical reaction which takes place when diluting sulfuric acid is poured over zinc granules.
Answer:
When the dilute sulfuric acid is poured over zinc granules, hydrogen gas is evolved and the mixture becomes hot. Hence, “evolution of a gas” and “change in temperature” are the two characteristics of this chemical reaction.
Question 3: Give two characteristics of the chemical reaction which occurs on adding potassium iodide solution to lead nitrate solution.
Answer:
On adding potassium iodide solution to lead nitrate solution, yellow precipitates of lead iodide are formed and the colour of the solution changes from colourless to yellow. Hence, “formation of a precipitate” and “change in colour” are the two characteristics of this chemical reaction.
Question 4: State one characteristic of chemical reaction which takes place when lemon juice is added gradually to potassium permanganate solution.
Answer:
When lemon juice is added gradually to potassium permanganate solution, there is a change in colour from purple to colourless. Hence, this reaction is characterized by a “change in colour”.
Question 5: State one characteristic of chemical reaction which takes place when quick lime is treated with water.
Answer:
When quicklime is treated with water, slaked lime is formed with the evolution of a large amount of heat. Hence, this reaction is characterized by a “change in temperature”.
Question 6: State one characteristic of chemical reaction which takes place when the wax is burned in the form of a candle.
Answer:
When the wax is burnt in the form of a candle, it produces water and carbon dioxide. Hence, this reaction is characterized by the “evolution of gas”.
Question 7: State one characteristic of chemical reaction which takes place when diluting hydrochloric acid is added to sodium carbonate.
Answer:
When sodium carbonate is added to dilute hydrochloric acid, carbon dioxide gas evolves. Hence, this reaction is characterized by the “evolution of gas”.
Types of Chemical Reactions as the name suggests explores the classification of various types of chemical reactions based on different parameters. As we are surrounded by chemical reactions in our daily lives. From burning a match stick to making food all of the things and events in our lives involve various types of chemical reactions. Understanding the different types of chemical reactions is key to understanding how matter changes and interacts with one another. From combustion reactions that power our cars and homes, to acid-base reactions that occur in our bodies and the natural world, there are many different types of chemical reactions with a wide range of applications
Combination, decomposition, single-replacement, double-replacement, redox, combustion, precipitation, neutralization, etc. are some of the types of chemical reactions using various parameters as the basis. In this article, we will learn about it all the types of chemical reactions and the various bases for these classifications of chemical reactions as well.
What is Chemical Reaction?
A chemical reaction is a process in which the bonds are broken within reactant molecules, and in order to form a new substance which is the result of new bonds formation in product molecules. This can be seen in a chemical reaction as the change in state, change in color, the evolution of gas, and change in temperature.
The changes in the chemical reaction can be classifed as physical or chemical change, and the detailed description of the same is as follows:
Physical change: When a usually reversible change in the physical properties of a substance, as size or shape takes place. Freezing a liquid, melting of candle, crushing a can, shredding papers all are examples of physical change.
Chemical change: When a chemical property of matter changes it is a type of chemical change such properties are density change, change in temperature, energy change etc, It is commonly called a chemical reaction. Combustion, rusting, fermentation, etc. are examples of chemical change.
Classification of Chemical Reactions
Based on the different properties, types of change or reactants,s and products, we can classify chemical reactions. Some of these classifications on various basis are as follows:
Based on Product and Reactant
Based on the formation of different kinds of products or change in the condition of reactants, different types of chemical reactions are:
Combustion reaction
Neutralization reaction
Decomposition reaction
Redox Reaction
Double-Displacement Reaction
Combination Reaction
In the Combination Reaction, two or more reactants combine together to form a single product. As in this reaction, new compounds are formed with the help of other compounds, so it is also called a synthesis reaction.
Some Examples of combination reactions are as follows:
Reaction of quick lime (Calcium Oxide) with water, results in calcium hydroxide,
CaO(s)+H2O(l)→Ca(OH)2(aq)
Reaction of sulfur trioxide gas with water results in sulfuric acid,
SO3(g)+H2O(l)→H2SO4(aq)
Note: This reaction is the reason behind the acid rain, as oxides of sulfur and nitrogen reaction with water in the atmosphere the acid produces and this acid-infused rain poured down on the surface of the earth which is called acid rain.
Decomposition Reaction
In the Decomposition reaction, a single component breaks down into two or more products, to break the bonds between different components a lot of heat is required, we can provide it in the form of heat, electricity or sunlight, etc.
Some examples of decomposition reactions are as follows:
Decomposition of carbonic acid,
H2CO3(aq) → H2O(l) + CO2(g)
Decomposition of Nickel (III) Oxide,
2Ni2O3(aq) → 4Ni(s) + 3O2(g)
The decomposition of calcium carbonate (CaCo3) gives CaO (Quick Lime) which is a major component of cement.
CaCO3(s) heat > CaO(s) + CO2(g)
Calcium hydroxide (Slaked lime) on decomposition gives Quick lime (CaO).
Ca(OH)2heat> CaO(s) + H2O (l)
Redox Reaction
Redox Reaction which is also called Reduction-oxidation reaction is the reaction, in which reduction(gain of the electron) and oxidation (loss of electron) takes place simultaneously. So in other words, it is the process of transfer of electrons between different elements and compounds to form new compounds.
Consider an example of an electron-chemical cell-like redox reaction between Zinc and Hydrogen.
Zn + 2H+ → Zn2+ + H2
For example, take the reaction of Iron with copper sulfate,
CuSO4 (aq) + Fe(s) → FeSO4 (aq) + Cu(s)
In the above reaction, a Zinc atom reacts with two positively charged hydrogen to which electrons get transferred from the zinc atom and hydrogen becomes a stable molecule and Zinc ion as the product.
Oxidation – Oxidation is a loss of electrons and the oxidation state of given reactant increases. In the above reaction, copper goes through oxidation as it gains electrons and is a reducing agent in this example.
Reduction – Reduction is a gain of electrons and the reactant state of a given reactant decreases. In the above reaction, iron goes through reduction as it losses electrons and is an oxidizing agent in this example.
Displacement Reaction
In a Single Displacement Reaction, more reactive metal displaces less reactive metal from its salt or other compounds. In these reactions, through reactivity series, products can be determined. Reactivity series is a series of elements in which elements are arranged in decreasing order of their reactivity. Thus, the elements present at the top of the series are more reactive than the elements present at the bottom of the series.
For example, take the reaction between potassium and magnesium chloride (MgCl2).
2K + MgCl2 → 2KCl + Mg
In this reaction, potassium displaces magnesium from its salt because of the more reactivity of potassium than magnesium. Potassium is present at the top of the reactivity series and hence, it is the most reactive element.
Some more examples of Single Displacement Reactions include:
Zinc reacting with hydrochloric acid to produce zinc chloride and hydrogen gas:
Zn + 2HCl → ZnCl2 + H2
Iron reacting with copper sulfate to produce copper and iron sulfate:
Fe + CuSO4 → Cu + FeSO4
Zinc reacting with silver nitrate to produce zinc nitrate and silver:
Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
Double-Displacement Reaction
It is a kind of displacement reaction in which two chemical species react and consequently, their ions i.e. cations and anions switch places forming two new products. now look at the reaction between silver nitrate and sodium chloride. The products of the reaction will be silver chloride and sodium nitrate after the double-displacement reaction.
Examples of double displacement reactions are as follows:
Reaction between silver nitrate and sodium chloride, results in silver chloride and sodium nitrate,
AgNO3 (aq)+ NaCl (s) → AgCl (aq) + NaNO3 (s)
Reaction between potassium nitrate and aluminium chloride, results in aluminium nitrate and potassium chloride,
KNO3 + AlCl3 → Al(NO3)3 + KCl
Reaction between sodium sulfate and barium chloride, results in barium sulfate and sodium chloride.
Na2SO4 (aq) + BaCl2 (aq) → BaSO4 (s) + 2NaCl(aq)
Based on Heat Involved in Reaction
Based on the heat involved in the chemical reaction, Reactions can be classified into two categories:
Exothermic Reaction
Endothermic Reaction
Exothermic reaction
Chemical reactions in which heat energy is released are known as exothermic reactions. The burning of methane gas in the presence of air produces heat energy. All the combustion reactions are exothermic.
For example, the combustion of ethane gives Carbon dioxide and water with some heat as well
2C2H6 (s) + 5O2 (g) → 2CO2(g) + 6H2O (g) + heat
Endothermic reaction
Chemical reactions that involve the absorption of energy are known as endothermic reactions.
Example: Formation of nitric oxide during the reaction of nitrogen and oxygen.
N2 (g) + O2 (g) + Heat → 2NO
Some Other Chemical Reactions
Other than all the above-mentioned types, there are some more important types of reactions that are used throughout the study of chemistry. These types are explained as follows:
Precipitation Reaction
A precipitation reaction is a type of chemical reaction that occurs when two solutions are mixed and a solid substance (precipitate) is formed as a result of the reaction. In this type of reaction, the ions of two different aqueous solutions react with each other to form an insoluble solid. This solid substance is called a precipitate and it settles at the bottom of the container.
An example of a precipitation reaction is the reaction between silver nitrate (AgNO3) and sodium chloride (NaCl):
AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)
In this reaction, silver nitrate and sodium chloride are mixed together, and the silver ions (Ag+) and chloride ions (Cl-) react with each other to form solid silver chloride (AgCl), which appears as a white precipitate. The sodium and nitrate ions remain in the solution as they do not react with each other.
Neutralization Reaction
A Neutralization reaction is a reaction between an acid and a base to give salt and water as the products. The formation of the water molecules is by the combination of OH– ions and H+ ions. The overall pH of the products when a strong base and a strong acid undergo a neutralization reaction must be 7. Consider the example of the neutralization reaction between Hydrochloric acid (HCl) and Sodium Hydroxide (NaOH) giving out sodium chloride (Common Salt) and water.
HCl (l) + NaOH (aq) → NaCl (aq) + H2O (l)
Combustion Reaction
A combustion reaction is a type of chemical reaction between a fuel and an oxidant that produces a product called ad oxidized product. an oxidizer is a chemical fuel required to burn such as oxygen. Generally, it’s a reaction between hydrocarbon and oxygen to yield carbon dioxide, water, and heat.
Hydrocarbon + Oxygen → Carbon dioxide + Water + Heat
For example, consider the combustion of methane gas,
Question 1: Guess the type of reaction given below:
CH4 + 2O2 ⇢ CO2 + 2H2O + Energy
Answer:
The above two reactions are combustion reaction.
Question 2: Define exothermic and endothermic reactions.
Answer:
An exothermic reaction is a reaction in which there is an release of energy which can be in the form of light or heat. Few examples are nuclear fission, rusting of iron.
On the other hand, an endothermic reaction is the reaction in which the system absorbs heat from the surrounding in the form of heat. Few examples are melting of ice, cooking etc.
Question 3: Define the term Reactant and Product.
Answer:
Reactant- The molecules or chemical species that react to form a product is known as reactant.
Product- The resultant species that formed after the reaction is known as Product.
Question 4: In the given reaction, identify the substance which gets oxidized and which gets reduced:
MnO2 + 4HCl → 2H2O + Cl2
Answer:
In the above equation HCl is oxidized to Cl2 and MnO2 is reduced to H2O, hence HCl is oxidized and MnO2 is reduced in the above reaction.
Question 5: Find the oxidizing agent for the following reaction:
H2S + I2 → 2HI + S.
Answer:
Addition of hydrogen is known as reduction whereas the reactant which get reduced is known as oxidizing agent. It is clear that I2 is reduced and hence it is an oxidizing agent.
Question 6: Why does the color of copper sulfate (CuSo4) solution change when an iron nail is dipped in it?
Answer:
When an iron nail is dipped in copper sulfate (CuSO4) solution, the displacement reaction takes place. The color of copper sulfate solution disappears due to the formation of light green solution of iron sulfate.
Fe(S) + CuSO4(aq) ⇢ FeSO4(aq) + Cu(S)
Question 7: Which reaction is called the opposite of combination reactions? Write equations for these reactions.
Answer:
Decomposition reaction, is known as the opposite of combination reactions, In this reaction single compound breaks down to produce two or more simpler substances.
For example, decomposition of Water, when electricity is condected through the water using electrodes.
2H2O (l) + Electricity ⇢ 2H2 (g) + O2 (g)
On the contrary, in combination reaction when two or more substances combine to form a new substance.
For example,
2H2 (g)+ O2 (g) ⇢ 2H2O(l)
FAQs on Types of Chemical Reaction
Q1: Define Chemical Reaction
Answer:
A Chemical Reaction is defined as the process in which atoms get rearranged by breaking older bonds and forming new bonds.
Q2: What are the different types of Chemical Reactions?
Answer:
There are different types of chemical reactions some of which are synthesis, decomposition, single displacement, double displacement, combustion, and redox reactions.
Q3: What is a Synthesis Reaction?
Answer:
A synthesis reaction is also called a combination reaction, and in this two or more compounds combine together to form a new compound.
Q4: What is a Decomposition Reaction?
Answer:
When a single compound breaks into smaller compounds than that is called a decomposition reaction.
Q5: What is a Displacement Reaction?
Answer:
Single displacement reactions are reactions in which more reactive elements displace another element from its salt or other compounds.
Q6: What is a Double Displacement Reaction?
Answer:
A double displacement reaction is a type of chemical reaction in which the cations and anions of two different compounds switch places to form two new compounds.
Q7: What is a Combustion Reaction?
Answer:
In combustion reactin compound reaction with oxygen and produce heat and light.
Q8: What is a Redox Reaction?
Answer:
If in a reaction reduction and oxidation occurs simultaneously, then that reaction is called a redox reaction.
Chemical Equations: As there are so many chemical reactions all around us, a nomenclature was created to make expressing a chemical reaction in the form of a chemical equation easier. A chemical equation is a mathematical statement that represents the production of a product from reactants while also indicating the conditions under which the reaction was carried out.
The reactants are on the left, and the products are on the right, with one-headed or two-headed arrows connecting them. Consider a reaction.
A + B → C + D
Here,
A and B are the reactants, and
C and D are the products of their reaction.
Reactants are identified in a chemical equation by their chemical formula. A chemical equation must be balanced to ensure the law of conservation of mass, which means the number of atoms on both sides must be equal. This is the method by which the equation is balanced.
A chemical reaction’s two main components are reactants and products. Reactants are substances that initiate a chemical reaction. The chemical species that can be detected after the reaction has been completed are referred to as products. Chemical reactions are classified into three types: acid-base reactions, redox reactions, and combustion reactions.
As a result, depending on the kind of reaction, the same reactant may produce multiple products at times. The primary difference between reactants and products is that reactants are consumed during the reaction, whereas products are produced as a result of the reaction.
What are Reactants?
Reactants are chemical species that serve as the catalyst in a chemical reaction. During the course of a chemical reaction, reactants are consumed.
None of the reactants may be present in the reaction mixture at the conclusion of the reaction, although some of the reactants may be present at the end.
Colourless or coloured reactants can exist. Depending on the nature and circumstances of the reaction, they can produce either colourless or coloured compounds. A chemical reaction’s reactants might exist in solid, liquid, or gaseous phases. Reactants differ depending on the sort of response.
Types of Reactions and Reactants
Combustion Reactions: Combustion reactions produce reactants that are extremely flammable chemical species.
Decomposition Reactions: Reactants in decomposition reactions are larger molecules than the products of the reaction.
Acid-Base Reactions: Acids and bases are the reactants in these reactions.
Redox Reactions: Oxidizing and reducing agents are the reactants. Buffer solutions are sometimes employed to keep the pH of the reaction mixture stable.
Synthesis Reactions: Synthesis processes use smaller molecules as reactants than they do as products.
Precipitation Reactions: The reactants of precipitation reactions are usually liquids.
Exothermic Reactions: The potential energy of the reactants in these chemical processes is greater than that of the products.
Endothermic Reactions: The potential energy of the reactants in these reactions is lower than that of the products.
What are Products?
Products are substances that are created as a result of a chemical reaction. These byproducts may be ions or molecules. The result of a chemical reaction might exist in the solid, liquid, or gaseous phases.
Colourless or multicoloured products are available. The colour of the result is determined by the type of reactants used in the reaction. The number of products present in a reaction mixture always rises as the reaction progresses.
Types of Reactions and Products
Combustion Reactions: For complete combustion (of hydrocarbons), the products of combustion reactions are frequently carbon dioxide and water, and carbon monoxide for partial combustion.
Decomposition Reactions: The products of decomposition processes are smaller molecules than the reactants.
Acid-Base Reactions: These reactions invariably produce salt and water as byproducts.
Redox Reactions: The products are oxidised versions of reactants and reduced forms of reactants. Water is frequently used as a product.
Precipitation Reactions: Precipitation reactions produce solid precipitates or suspensions.
Synthesis Reactions: Synthesis reactions produce larger molecules than reactants.
Exothermic Reactions: The potential energy of the products of these chemical reactions is lower than that of the reactants.
Endothermic Reactions: These reactions’ products have higher potential energy than the reactants.
Examples of Reactants and Products
In a reaction, reactants are what you start with. They differ from what you get after the reaction takes place. Any chemical reaction involves both reactants and products.
The wax of a candle and the oxygen in the air are reactants in a combustion reaction. Carbon dioxide and water vapour are the byproducts.
When methane gas is burned, the reactants are methane (CH4) and oxygen in the air (O2). The reaction produces carbon dioxide (CO2) and water (H2O).
The reactants in the formation of water are hydrogen (H2) and oxygen (O2) gas. Water is the product (H2O).
Carbon dioxide (CO2) and water are the reactants in photosynthesis (H2O). Glucose is the product (C6H12O6). It should be noted that sunlight is not a reactant. Reactants are matter (atoms, molecules, and ions) rather than energy.
Identifying Reactants and Products in Chemical Equations
To identify the reactants and products in a chemical equation, look at the reaction arrow. The arrow points from left to right in a reaction that only proceeds forward. The reactants are on the left side of the arrow, while the products are on the right. A chemical species that appear on both sides of a reaction (such as solvent or spectator ions) is neither a reactant nor a product. In the following reaction, A and B are reactants, and C is the product:
A + B → C
There does not, however, have to be more than one reactant. A is the reactant in this reaction, while B and C are the products:
A → B + C
In a balanced chemical equation, the number and type of atoms are the same for the products and the reactants. For example, the number of hydrogen and oxygen atoms in the reactants (H2 and O2) and the product is the same (H2O).
Difference Between Reactant and Product
Reactants
Products
Chemical reactants are the starting element for a chemical reaction.
Products are the byproducts of chemical reactions.
Reactants are consumed throughout the process.
The reaction’s products are not absorbed.
During the response, the quantity of reactants in the reaction mixture decreases quickly or slowly.
The quantity of products present in the reaction mixture increases rapidly or gradually.
At the start of the reaction, only reactants are present.
At the start of the reaction, no products emerge in the reaction mix.
At the end of the reaction, reactants may or may not be present in the solution combination.
At the end of the reaction, the products are discovered in the solution blend.
Sample Questions
Question 1: What is meant by a chemical reaction?
Answer:
A chemical reaction occurs when two or more molecules collide with the proper orientation and enough force to form a new product. This process involves the breaking and forming of atom bonds. Compounds that interact to form new compounds are referred to as reactants, while the newly formed compounds are referred to as products.
Question 2: What is electrolytic decomposition?
Answer:
Electrolytic decomposition is the process of decomposing any molecule using electricity. This is useful when we need to separate molecules that dissociate at high temperatures. Sodium chloride is one such example. Sodium chloride dissociates at high temperatures but easily breaks apart during electrolytic decomposition.
Question 3: Differentiate between single displacement and double displacement reactions?
Answer:
A single displacement reaction occurs when one or more elements in a compound replace another element. A double displacement reaction, on the other hand, involves two ion exchanges between compounds, resulting in the formation of two new compounds.
Question 4: How do we balance a chemical equation?
Answer:
Make a note of the unbalanced chemical reaction. If the unbalanced chemical reaction is not given, write down the skeletal equation using the components of the chemical reaction that are mentioned.
Take note of how many atoms are on each side of each element’s reaction. The number of atoms is represented by an element’s subscript. If the number of atoms on the reactant side is not equal to the number of atoms on the product side, the equation is not balanced. Because this violates the law of conservation of mass, we must balance the chemical reaction.
In the chemical reaction, add coefficients to the compounds or elements so that the number of atoms on both sides of the reaction matches for all constituent elements. Keep in mind that oxygen and hydrogen atoms should be balanced last because they are present in a variety of compounds and trying to fix that ratio first will complicate things even more.
Question 5: What is the difference between reactant and reagent?
Answer:
Reactant and reagent are terms that are frequently used interchangeably. Technically, the two words do not have the same meaning. In analytical chemistry, a reagent is a substance that is added to cause a chemical reaction or to test whether one has occurred. Reagents are not always consumed in a reaction. Although solvents, catalysts, and substrates may be present in a reaction, they are not considered reactants or products.
Short-Hand Method of Representing a Chemical Reaction.
A chemical equation is a means of describing a chemical reaction using symbols and equations for the substances involved in the process. The example below demonstrates how to clearly understand the meaning of a chemical equation.
Zinc sulphate and hydrogen gas are formed when zinc metal combines with dilute sulphuric acid. This reaction can be expressed in words as follows:
Zinc + Sulphuric acid → Zinc sulphate + Hydrogen
This is referred to as a word equation. By writing the symbols and formulae of the various substances in place of their names, we may convert this word equation to a chemical equation.
The symbol of zinc is Zn.
The formula of sulphuric acid is H2SO4.
ZnSO4 is the formula of zinc sulphate.
H2 is the formula of hydrogen.
We derive the following chemical equation by placing the symbols and formulas of all the chemicals in the above word equation.
Zn + H2SO4 → ZnSO4 + H2 Reactants Products
Reactants are compounds that mix or react together. Zinc and sulphuric acid are the reactants in the above reaction. In an equation, the reactants are always written on the left side with a plus sign (+) between them.
Products are the new substances produced during a reaction. The products of the reaction are zinc sulphate and hydrogen. In an equation, the products are always written on the right side, with a plus symbol (+) between them.
Between the reactants and the products, an arrow sign (→) pointing to the right is placed. This arrow indicates that the substances on the left-hand side of the equation are combined to produce the substances on the right-hand side. It should be obvious by now that the chemical equation is a shorthand method of representing a chemical reaction.
Balanced Chemical Equation
In a balanced chemical equation, the reactants and products have an equal number of atoms of different elements. In other words, on both sides of a balanced chemical equation, the number of atoms of the various elements is equal. The following example will help to clarify this point.
Zinc sulphate and hydrogen are formed when zinc combines with dilute sulfuric acid. This can be written as an equation:
Zn + H2SO4→ ZnSO2 + H2
In the following table, let’s count how many atoms each element has in the reactants and products individually.
Number of atoms of elements
In reactants
In products
Zn
1
1
H
2
2
S
1
1
O
4
4
We found that the reactants and products both contain one zinc atom. Two hydrogen atoms are found in reactants and two hydrogen atoms are found in products. Reactants and products each have one sulphur atom in them. Finally, the reactants have four oxygen atoms, and the product has four oxygen atoms as well. As a result, the reactants and products have an equal number of atoms of different elements, making the above-mentioned chemical equation balanced. A balanced chemical equation contains equal masses of various elements in reactants and products because the number of atoms of various elements in reactants and products is equal.
Unbalanced Chemical Equation
The reactants and products in an unbalanced chemical equation have an uneven number of atoms of one or more elements. An unbalanced chemical equation, in other words, has an uneven number of atoms of one or more elements on both sides. The following example will help to clarify this point.
Water is formed when hydrogen combines with oxygen. This reaction can be expressed by the equation as.
H2 + O2→ H2O
In the following table, let’s count how many hydrogen and oxygen atoms there are in the reactants and products.
Number of atoms of elements
In reactants
In products
H
2
2
O
2
1
In this equation, the reactants have two hydrogen atoms, and the products have two hydrogen atoms as well. However, the reactants and products have different numbers of oxygen atoms. The reactants, on the left side, have two oxygen atoms, but the products, on the right side, have just one. The preceding chemical equation is unbalanced because the number of oxygen atoms in the reactants and products is uneven. Due to the uneven number of atoms of various elements in reactants and products, it can be said that an imbalanced equation is one in which the masses of various elements in the reactants and products are uneven.
Sample Questions
Question 1: What distinguishes chemical reactions from other types of reactions?
Answer:
Chemical reactions have a number of essential features.
A gas’s evolution.
Precipitation is the formation of a substance.
A colour change takes place.
The temperature change.
The state change.
Question 2: Why should chemical equations be balanced?
Answer:
To satisfy the law of mass conservation in chemical reactions, the chemical equations must be balanced.
Question 3. Is the following equation balanced or unbalanced?
CH4 + O2→ CO2 + H2O
Answer:
In a balanced chemical equation, the reactants and products have an equal number of atoms of different elements.
The reactants and products in an unbalanced chemical equation have an uneven number of atoms of one or more elements.
There is 1 atom of carbon atom in the reactants as well as in the products. There are 4 atoms of hydrogen in the reactants but there are 2 atoms of hydrogen in the products. Also, there are 2 atoms of oxygen in the reactants but there are 3 atoms of oxygen in the products. Since there is an uneven number of atoms of hydrogen and oxygen in the reactants and products. Hence the above reaction is unbalanced.
Question 4: A chemical reaction is balanced on what basis?
Answer:
A chemical reaction is said to be balanced if the reactants and products have an equal number of atoms of different elements.
Question 5. What is the law of mass conservation?
Answer:
The law of conservation of mass states that matter cannot be generated or destroyed in a chemical reaction, and as a result, in a chemical reaction, the number of atoms of various elements in reactants and products must be equal.
Endothermic Reactions Endothermic reactions are defined as those in which heat is absorbed. When nitrogen and oxygen are heated to around 3000°C, they combine to generate nitrogen monoxide, and a significant amount of heat is absorbed in the process. N2 + O2→ 2NO (Nitrogen) (Oxygen) (Nitrogen monoxide) Since heat is consumed in the reaction between nitrogen and oxygen to generate nitrogen monoxide, it is an endothermic reaction. On the reactants’ side of an equation, write “+Heat” and “+Heat energy” or just “+Energy” to indicate an endothermic reaction. The image given below shows the potential energy and rate of reaction curve of the Endothermic Reactions. Here ∑HP and ∑HR are the sums of enthalpies of the products and reactants, respectively, and ΔH is the change in the enthalpy during a reaction, i.e., ΔH = ∑HP – ∑HR. Ea is the activation energy of the reaction. Examples of Endothermic Reactions Various examples of Endothermic reactions are, Heating of Calcium Carbonate When calcium carbonate is heated, for example, it decomposes into calcium oxide and carbon dioxide. CaCO3 + Heat → CaO + CO2 (Calcium carbonate) (Calcium oxide) (Carbon dioxide) Since heat energy is absorbed in the decomposition of calcium carbonate, it is an endothermic reaction. Photosynthesis Reaction Photosynthesis is an endothermic reaction, where green plants absorb sunlight in presence of carbon dioxide, and water gives carbohydrates and oxygen as products. 6CO2 + 6H2O + sunlight → C6H12O6 + 6O2 The endothermic reaction can be written as follows in a chemical equation: Reactants + Energy → Products Endothermic reactions are chemical processes in which the reactants absorb heat from the surroundings. These reactions cause a cooling effect by lowering the temperature of the surrounding environment. Endothermic reactions are characterized by the creation of chemical bonds as a result of heat absorption from the environment. Exothermic reactions, on the other hand, involve the release of heat energy generated by the bond breakdown. The energy change or enthalpy change in an endothermic reaction is positive, i.e., ΔH > 0. Exothermic Reactions A chemical reaction that involves the release of energy in the form of heat or light is known as an exothermic reaction. For example, when carbon burns in presence of oxygen to make carbon dioxide, a large amount of heat is produced. C + O2 → CO2 + Heat (Carbon) (Oxygen) (Carbon dioxide) Since heat is produced during the combustion of carbon in oxygen, it is an exothermic reaction. On the products’ side of an equation, use “+Heat” or “+Heat Energy” or simply “+Energy” to indicate an exothermic process. The image given below shows the potential energy and rate of reaction curve of the Exothermic Reactions. Here ∑HP and ∑HR are the sums of enthalpies of the products and reactants, respectively, and ΔH is the change in the enthalpy during a reaction, i.e., ΔH = ∑HR – ∑HP. Ea is the activation energy of the reaction. Examples of Exothermic Reactions Various examples of Exothermic reactions are, Burning of Natural Gas Methane is the major component of natural gas. When natural gas is burned in the presence of oxygen in the air, carbon dioxide and water vapour are produced. There is also a significant amount of thermal energy produced. The following is an example of how this could be expressed: CH4 + 2O2→ CO2 + 2H2O + Heat energy (Methane)(Oxygen)(Carbon dioxide)(Water) Since heat is produced during the combustion of natural gas, it is an exothermic reaction. Exothermic reactions characterize all combustion reactions. For example, the combustion of fuels such as wood, coal, kerosene, gasoline, and diesel, are all exothermic reactions since they produce heat energy. Breaking of Food Food is broken down into simpler components during digestion. The main component of food is carbohydrates and it is found in chapati, bread, rice, and potatoes. Carbohydrates are broken down into simple carbohydrates called glucose during digestion. In a process known as respiration, this glucose is slowly burned by mixing with oxygen in our body’s cells to make energy. This energy also keeps our bodies warm, among other things. During respiration, glucose interacts with oxygen in our body’s cells to produce carbon dioxide, water, and energy. C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy These reactions are the polar opposites of endothermic reactions, and they can be written as follows in a chemical equation: Reactants → Products + Energy As a result, it’s easy to see how the net amount of energy required to start an exothermic process is less than the net amount of energy released. The changes in enthalpy for an exothermic reaction will always be negative., i.e. ΔH < 0. Why is Heat Released or Absorbed in a Chemical Reaction? Chemical reactions occur when a chemical compound changes its chemical composition. Chemical compounds are made when various molecule joins together using chemical bonds. These bonds involve energy change either to form the bonds or break the bond. When chemical bonds are formed, energy is released in form of heat, and when chemical bonds are broken, energy is absorbed from the surrounding. Difference between Endothermic and Exothermic Reactions The words ‘Endo’ and ‘Exo,’ which mean ‘within’ and ‘out,’ respectively, have Greek roots. The major difference between endothermic and exothermic reactions, as their names suggest, is that the former absorbs heat from the surroundings while the latter releases it. The following table gives the difference between Endothermic and Exothermic Reactions, Exothermic Reaction Endothermic Reaction A reaction that releases heat as a type of energy from the system. A reaction in which the system absorbs energy in the form of heat from its surroundings. The system’s energy is released into the environment. The energy from the surroundings is absorbed into the reaction. Heat, electricity, light, and sound are forms of released energy. Energy is absorbed in form of energy. Examples include rusting iron, settling, chemical bonds, explosions, and nuclear fission. Examples include ice melting, evaporation, cooking, gas molecules, and photosynthesis.
What is a Decomposition Reaction?
The decomposition reaction is just the opposite of the combination reaction. In a combination reaction, a substance is formed as a result of a chemical combination however, in a decomposition reaction, the substance breaks into new substances. The energy required for breaking down of product can be in the form of heat, light, or electricity. Let’s learn the definition of decomposition reaction in the following paragraph.
Decomposition Reaction Definition
We can define a decomposition reaction as “A decomposition reaction is a chemical process in which the molecule or reactant breakdown into simpler products. Thus, when one reactant breaks down into two or more products.”
For example, by heating calcium carbonate it breaks down into calcium oxide and carbon dioxide gas. The balanced reaction of this can be written as follows:
For any compound AB, the general equation of the decomposition reaction can be given as:
AB → A + B
In the above reaction, AB represents the reactant which is a chemical compound of A and B that starts the reaction, while A and B represent the products obtained by the reaction. and the arrow represents the direction in which the reaction occurs.
Decomposition Reaction Examples
Here are some important examples of Decomposition Reactions:
Electrolysis of Water
The electrolysis process is an excellent example of a decomposition reaction. The reaction takes place by breaking down molecules by passing electricity.
H2O (l) ⇢ 2H2 (g)+ O2 (g)
Decomposition Reaction of Hydrogen Peroxide
Hydrogen peroxide breaks down into water and oxygen in the presence of light, as shown below:
Decomposition Reaction of KClO3
The decomposition reaction of potassium chlorate (KClO3) can be represented by the following balanced chemical equation:
2KClO3(s) → 2KCl(s) + 3O2(g)
In this reaction, solid potassium chlorate (KClO3) decomposes into solid potassium chloride (KCl) and oxygen (O2). The reaction is typically initiated by potassium chlorate, which provides the energy required for the decomposition to occur.
Decomposition Reaction of Metal Carbonates
When metal carbonates are heated, it gets decomposed into their metal oxides and carbon dioxide. For Example, Calcium carbonate get decomposed to Calcium oxide and Carbon Dioxide while, Sodium Carbonate get decomposed to Sodium oxide and Carbon Dioxide, as shown below:
Decomposition Reaction of Metal Hydroxides
On heating, metal hydroxides break down into metal oxides and water. Thus, Water and sodium oxide is produced during the breakdown of sodium hydroxide, as shown below:
Decomposition Reaction of Oxy Acids
The decomposition of oxy acids leads to the production of carbon dioxide and water as shown below:
Types of Decomposition Reaction
The decomposition reactions are majorly classified into three types:
Thermal Decomposition Reaction
Electrolytic Decomposition Reaction
Photo Decomposition Reaction
Thermal Decomposition Reaction (Thermolysis)
A single substance can split into two or more simple substances when heated in a chemical process known as thermal decomposition. Since heat is necessary to break the substance’s bonds, the reaction is usually endothermic.
For example, when potassium chlorate is heated it decomposed into potassium chloride and oxygen i.e.,
When an electric current is passed through an aqueous solution of a substance, electrolytic decomposition may occur. Water electrolysis works as a good example of an Electrolytic Decomposition Reaction (shown below).
Photo Decomposition Reaction
Photo decomposition is a chemical reaction in which a chemical compound is split up into simple substances by exposure to light (photons).
For example, when a small amount of silver chloride (AgCl) is taken in a watch glass and exposed to the sun for a while. The crystals gradually start to turn grey. Analysis reveals that silver chloride has broken down into silver and chlorine due to sunshine as shown below:
Double Decomposition Reaction
A double replacement reaction is a reaction between two compounds in which the positive ion of one molecule is exchanged for the positive ion of the other component. One or more of the reactants in a double decomposition reaction is insoluble in the solvent, which is a type of double displacement reaction.
A double decomposition reaction is a reaction between two compounds in which components of each substance are exchanged out to create two new compounds.
For example, zinc chloride and hydrogen sulphide gas are produced when zinc sulphide and hydrochloric acid react. There, zinc sulphide is both solid and undissolved in an aqueous medium.
Uses of Decomposition Reactions
Various uses of the Decomposition reaction are,
Decomposition reactions are widely used to extract the metal.
Decomposition reactions help to manufacture cement or calcium oxide.
The decomposition reaction cause the fizz in a soda bottle.
This reaction is very helpful to break down hazardous waste.
Also, it is important for the human digestive system to digest food.
Combination Reaction Vs. Decomposition Reaction
There are some key differences between both combination and decomposition reactions. Some of these differences are as follows:
Property
Combination Reaction
Decomposition Reaction
Definition
A reaction where two or more substances combine to form a single product.
A reaction where a single compound breaks down into two or more simpler substances.
Reactants
Two or more elements or compounds.
A single compound.
Products
A single compound.
Two or more elements or compounds.
Energy Change
Often release energy in the form of heat or light.
Often require an external energy source (such as heat) to initiate the reaction.
Example
2Mg + O2 → 2MgO
2H2O2 → 2H2O + O2
Decomposition Reaction in our Body
A chemical reaction is a process of changing one substance into another. Living bodies also depend on these reactions for proper functioning, nutrient gain, digestion, growth, etc. When we see the functioning of our body everything depends on chemical reactions. Digestion is the process of breaking down molecules or food into simpler forms. The salivary glands secret a special chemical substance called enzyme which helps in the breakdown. The starch of food decomposes into glucose in the body.
The reactant or organic food item consisting of carbohydrates, fats, and proteins is broken down into simpler products, and energy is also released. These products are carried throughout the body through the bloodstream for the functioning of the body.
Similarly, proteins are decomposed into simpler forms called amino acids which promote growth. Proteins are broken down into amino acids through hydrolysis. The amino acids are produced to dissolve in blood and are carried out throughout the tissues of the body.
Examples of Oxidation Reaction
The effects of oxidation reactions can be seen in a variety of ways in our daily lives. Some of them are advantageous, while others are detrimental. The following are some examples of oxidation reactions:
In our bodies, respiration is an oxidation reaction. During respiration, food is oxidized to produce energy.
Combustion Reactions: Any substance’s combustion or burning is an oxidation reaction in which energy is always produced. The combustion of various fuels is used as a source of energy in a variety of home and industrial activities.
Corrosion of active metals is one of the oxidation reactions.
Rancidity: Fried foods develop a foul odour and a terrible taste when exposed to air for an extended period of time.
Combustion Reactions
Kerosene, coal, charcoal, wood, and other materials float in the air and burn. When methane, a major component of natural gas, is heated, it burns with an excess of oxygen.
CH4 + 2O2 → CO2 + 2H2O
All combustion reactions in nature are exothermic and redox, which means they all emit heat energy. The human body can be compared to a furnace or machine that burns or oxidises various foods. As a result of the thermal energy that has been generated, our bodies continue to function. Carbohydrates like glucose, fructose, and starch are the body’s primary energy source. They, for example, are combusted with the oxygen we breathe to produce carbon dioxide and water.
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
In all combustion reactions, there is no flame. Combustion is simply oxidation with energy release. Respiration is the most important biological reaction that releases energy in cells. When we breathe, oxygen enters our lungs and passes through thousands of tiny air sacs (alveoli). These air sacs occupy a significant amount of membrane space, and oxygen diffuses into the blood through the membranes. It binds to haemoglobin in red blood cells before spreading to millions of cells throughout the body. Respiration occurs in these cells, along with the burning of glucose, which produces carbon dioxide and water.
Because the reaction is exothermic, the energy released during respiration powers many cell activities and keeps our heart and muscles working. It also achieves the desired results. It also provides the body with the necessary warmth. Carbon dioxide and water are both reabsorbed into the bloodstream before being exhaled. Respiration is a natural process that occurs in all living things’ cells. Fish use their gills to absorb oxygen dissolved in water, whereas plants absorb oxygen through microscopic pores (stomata) in their leaves.
Corrosion
Corrosion is a slow process in which the surfaces of metallic objects become coated with the metal’s oxides, hydroxide, carbonate, or sulphide. Metal is destroyed as a result of chemical or electrochemical reactions with the environment.
Corrosion is also defined as the gradual deterioration of metal surfaces caused by the action of air, moisture, or a chemical on their surface. It deteriorates (damages) buildings, bridges, ships, and metal objects, particularly iron. Corrosion can be seen in the following examples:
Development of green coating on copper
Tarnishing of silver
Rusting of iron
Corrosion of some Metals are listed below:
Copper: When exposed to a humid environment, copper articles develop a coating of green copper carbonate.
Silver: Silver loses its lustre and develops a black coating on its surface. This is because it oxidises to silver sulphide when it reacts with hydrogen sulphide in the air. This is also referred to as tarnishing silver.
Iron: Rusting of iron metal is the most common type of corrosion. When an iron object is exposed to moist air for an extended period of time, its surface becomes coated with rust, a brown, flaky, non-sticky substance.
Prevention of Corrosion
Metal corrosion is a serious issue, and various measures are taken to prevent it. The main principle underlying each method is to keep the metal surface away from moisture and air. The following are a few corrosion prevention methods:
Metal corrosion can be avoided by coating their surfaces with paint or varnish.
The application of oil or grease to moving parts of the machinery prevents corrosion.
Metal corrosion can also be avoided by coating the metal’s surface with non-corrosive metals. E.g. Copper corrosion can be avoided by coating it with tin, and metallic objects can be electroplated with noble metals such as silver and gold.
Metals, such as aluminium, can be coated with a thin, strong layer of oxides. It is protected from corrosion by this passive layer. Anodizing is the name given to this process.
Some metals can be protected from corrosion by converting them into alloys. Iron, for example, can be transformed into stainless steel.
Rusting of iron can also be avoided by coating its surface with a layer of a more reactive metal that prevents the oxidation of iron. Galvanization is a process in which zinc is used to cover iron. It is an effective method of protecting iron because the zinc protects it even if the surface is scratched.
Rancidity
Oxidation is harmful to our food and eatables. Atmospheric oxidation degrades stored foods containing fats and oils, rendering them unfit for human consumption. Foods containing fats and oils develop unpleasant odours and bad taste after a long period of storage due to aerial oxidation of fats and oils.
Rancidity refers to the slow aerial oxidation of fats and oils, which results in an unpleasant odour and taste.
These fats and oils are referred to as ‘rancid.’ Rancid fats and oils have an unpleasant odour and taste, and as a result, rancid foodstuffs should not be used because they are harmful to the human body; rancidity in foodstuffs is undesirable and must be controlled.
Methods of Preventing Rancidity
The oxidation of fats and oils in food is the primary cause of rancidity. Oils/fats containing food must be kept from oxidising in order to prevent rancidity. The following methods are used to prevent or delay rancidity:
The use of anti-oxidants slows down the oxidation of oil or fat in food. These are the substances that have a high proclivity to oxidation. These are oxidised and thus prevent the oxidation of food materials.
Packing in Nitrogen: In some packed foodstuffs, such as potato chips, the plastic bags are filled with the inert gas nitrogen, preventing oxidation and rancidity.
Keeping in Refrigerator: This is a common method in our household. When food is stored in a refrigerator, the oxidation of fats and oils in the food is slowed due to the low temperature, reducing the rate of rancidity.
Storing in Air-Tight Containers: When food is stored in airtight containers, it is exposed to very little oxygen, which slows the oxidation of fats and oils in the food and thus slows the rate of rancidity.
Storing Foods Away from Light: When food is stored away from light, the oxidation of fats and oils in the food is slowed, and thus the rate of rancidity is slowed.
Vacuum Packing: In many cases, the container is evacuated before sealing after the food has been packed. This is done because there will be no air or oxygen available to oxidise food and cause it to go rancid.
Sample Questions
Question 1: What is biological oxidation?
Answer:
Biological oxidation is a biological process in which electrons are lost, as opposed to reduction, which involves the gain of electrons. Oxidation and reduction, on the other hand, are linked as a redox reaction, which is an energy-producing reaction within the cell.
Question 2: What are the effects of oxidation reactions in everyday life?
Answer:
The loss of electrons or the addition of oxygen are both involved in oxidation reactions. Many processes in our daily lives, such as respiration, combustion, and photosynthesis in plants, involve oxidation. Fats and oils oxidise and become rancid as a result of this process. That is why potato packets are filled with nitrogen gas to keep them fresh for a long time; otherwise, oxidation causes them to go rancid.
Question 3: Suggest some methods to prevent rancidity.
Answer:
Use of anti-oxidants are:
Food packaging in nitrogen-gas flushed bags.
Storing food in refrigerators and in air-tight containers.
Keeping food away from sunlight.
Question 4: What are the effects of oxidation and reduction reactions?
Answer:
Any chemical reaction in which the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron is an oxidation-reduction reaction. Redox reactions are common and essential to some of life’s most basic functions, such as photosynthesis, combustion, and corrosion or rusting.
Question 5: What is an example of useful oxidation?
Answer:
The combustion or burning of any substance is an oxidation reaction in which energy is always created. The combustion of various fuels is used as a source of energy in a variety of home and industrial activities.
Question 6: Write a short note on corrosion.
Answer:
Corrosion is a slow process in which the surfaces of metallic objects become coated with the metal’s oxides, hydroxide, carbonate, or sulphide. Metal is destroyed as a result of chemical or electrochemical reactions with the environment. Corrosion is also defined as the gradual deterioration of metal surfaces caused by the action of air, moisture, or a chemical on their surface. It deteriorates (damages) buildings, bridges, ships, and metal objects, particularly iron.
