(a) What is a chemical equation? Explain with the help of an example.
(b) Giving examples, state the difference between balanced and unbalanced chemical equations.
(c) Balance the following chemical equations:
(i) ${NH}_3$ → $N_2+H_2$
(ii) C + ${CO}_2$ → CO

(a) The method of representing a chemical reaction with the help of symbols and formulae of the substances involved in it is known as chemical equation.
For example, zinc metal reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas.
This can be represented by chemical equation as follows:
Zn (s) + H₂SO₄ (aq) $\to$ ZnSO₄ (aq) + H₂ (g)

(b)

Balanced Chemical Equation	Unbalanced Chemical Equation
A balanced chemical equation has an equal numbers of atoms of different elements in the side of reactants and products.	An unbalanced chemical equation has an unequal number of atoms of one or more elements in the reaction.
In a balanced chemical equation the sum of masses of the reactants is equal to the sum of the masses of the products.	In an unbalanced chemical equation the sum of masses of the reactants is not equal to the sum of the masses of the products.
It obeys the law of conservation of mass	It does not obey the law of conservation of mass
Example: Zn (s) + H2SO4 (aq) $\to$ ZnSO4 (aq) + H2 (g) Here, number of Zn, H, S and O are same in both reactants' and products' side.	Example: H2 + O2 $\to$ H2O Here, one oxygen atom is more in reactant's side than in product's side; it means one atom of oxygen is being destroyed, which is a violation of law of conservation of mass.

(c) (i) 2NH₃ $\to$ N₂ + 3H₂

(ii) C + CO₂ $\to$ 2CO