Chapter-1

Chemical Reactions and Equations 

Chemical Equation:- Representing a chemical reaction using the symbols and chemical formulas of reactants and products is called a chemical equation.

E.g.- Zn + H2S04→ZnSO4 + H2 

Reactants:- Substances that take part in a chemical reaction. Are called reactants.

E.g.- Zn +  H2S04 

Products:- Substances that are obtained after the completion of a chemical reaction. Are called products.

E.g.- ZnSO4 + H2  

Balanced Chemical Equation:-

The chemical equation in which the number of atoms of different elements is the same in both the reactant and product sides. Is called a balanced chemical equation. 

E.g.-3Fe + 4H20→Fe304 + 4H2 

  2H2  +O2→2H2O 

Types of chemical reactions: - Chemical reactions are of the following types.

1. Combination reactions / conjugation reactions / addition reactions

2. Decomposition reactions / decomposition reactions

3. Exothermic reactions

4. Endothermic reactions

5. Displacement reactions

6. Double displacement reactions

7. Oxidation reactions / oxidation reactions

8. Reduction reactions

9. Redox reactions. Oxidation-reduction reaction

Combination reactions: - In this reaction, two or more reactants combine to form a single product. Such reactions are called combination reactions.

Example-

(1) Combustion of coal :- C+O2→CO2 

(2) Formation of water :- 2H2 +02→2H20 

(3) Combustion of sulphur    S+02→SO2 

(4) Formation of calcium hydroxide :- CaO + H20 →Ca(OH)2 

Decomposition reaction :- The reaction in which a single reagent combines to form two or more products is called decomposition reaction.

Example :-

(i) Decomposition reaction of ferrous sulphate

2FeSO4 → Fe203 + SO2 + SO3

CaCO3 

Is the formula of marble. 

(ii) Decomposition reaction of calcium carbonate

CaCO3→ CaO + CO2 

(iii) Silver bromide is also a type of decomposition reaction.

2 AgBr →2 Ag + Br2 

This reaction is used in black - white photography.

Exothermic reactions: - The reactions in which heat is released as energy are called exothermic reactions.

Example: -

(1) Combustion of natural gas

CH4 + 2O2→CO2 + 2H2O + energy

(ii) Respiration is an exothermic reaction

Humans need energy to survive. We get this energy from food. Food items break down during the digestion process. For example, rice, potatoes and bread contain carbohydrates. Glucose is obtained by breaking down carbohydrates. This glucose combines with oxygen present in the cells of our body and provides us energy. The name of this reaction is respiration.

C6H1206 + 602→6C02 + 6H20 + energy 

(ii) The decomposition of vegetables and compost is also an example of exothermic reaction.

Endothermic reactions: - The reactions in which energy is absorbed are called endothermic reactions.

Example: -

(i) H2  + I2 + energy→ 2HI2

(ii) N2 + 2O2 + energy → 2NO2

Displacement reaction -: Such reactions in which one atom or group of a molecule of a compound is replaced by another atom or group. These are called displacement reactions. Example:-

Zn + CuSO4→ ZnSO4 + Cu

Fe+ CuSO4→FeSO4 + Cu

Double displacement reactions:- Those reactions in which there is exchange of ions between reactants are called double displacement reactions.

Example:-

Na2S04 + BaCl2 →BaSO4 + 2NaCl 

Oxidation reactions:- Those reactions in which there is increase in oxygen and loss of hydrogen are called oxidation reactions.

Example:-

2Mg + O2 → 2MgO 

2Cu + O2 → 2CuO 

Reduction reactions:- Those reactions in which there is increase in hydrogen and loss of oxygen are called reduction reactions.

Example:-

CuO + H2→ Cu+ H20 

Redox reactions:- Chemical reactions in which oxidation and reduction reactions take place simultaneously are called redox reactions.

Example:-

CuO + H2 → Cu + H20 

Oxidation   Reduction

Effects of oxidation reactions in daily life:-

Corrosion:- When a metal comes in contact with acid, moisture etc. around it, then it corrodes. This process is called corrosion.

Example:- Black layer on silver, green coating on copper

Rusting on iron

Rice:- When oil and fat are oxidized, they become icy and their smell and taste change. This process can be prevented by adding antioxidants or by keeping the food items in sealed containers or by flowing nitrogen into them.

Example: Potato chips can be prevented from forming by flowing nitrogen into their bags.