Q2 of 41 Page 1

Why is it necessary to balance a chemical equation?

We know that, according to the law of conservation of mass, the total mass of all the atoms present in the reactants should be equal to that of all the atoms present in the products. This law will hold good only when the number of atoms of all types of elements on both sides is equal. Thus balancing of chemical equation is necessary so that the law of conservation of mass may be obeyed.

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1 What is the method of balancing chemical equation? 3 In the equations given below, state giving reasons, whether substances have been oxidised or reduced.
(i)  PbO + CO  →Pb + CO2 (ii) H2S + Cl2 →2HCl + S. 4 A sample of water weed was placed in water and exposed to sunlight. Bubbles of a gas are seen on the surface of the leaves.
(i) Name the gas evolved.
(ii) Name the process taking place.
(iii) Write a balanced equation of reaction taking place. 5 Give balanced equations, wherever possible, or where this is not possible, explain the following by means of examples:
(i) A reaction which gives out heat.
(ii) A reaction which takes place with the help of sunlight.
(iii) A reaction which is brought about by electric current.
(iv) Reversible Reactions.
(v) A reaction with a solid and gas which produces heat.