Question

4. (b) Explain how to balance a chemical equation by giving an example.

Answer 1

Part 1: Balanced Equation

An equation in which the number of each atom of an element on the reactants side is equal to the number of each atom of an element on the product side is called a balanced equation

Part 2: Example:

• Zinc reacts with hydrochloric acid to form zinc chloride and hydrogen gas.
• Zinc + hydrochloric acid → zinc chloride + hydrogen gas
• Writing the formulae of all the substances in the above equation:
• $\mathrm{Zn}+\mathrm{HCl}\to {\mathrm{ZnCl}}_2+{\mathrm{H}}_2$
• This is an unbalanced equation.

Part 3: Balancing the equation

• Counting the number of various atoms in reactants and products.

	Zinc atoms	Hydrogen atoms	Chlorine atoms
In reactants	1	1	1
In products	1	2	2

• Because the total number of chlorine atoms on the reactant side is 1, whereas on the product side is 2, and also the total number of hydrogen atoms on the reactant side is 1, whereas on the product side is 2.
• To make them equal, we need to multiply $\mathrm{HCl}$ by with numeral 2 on the reactant side. Therefore, the balanced equation will be:

$\underset{\mathrm{Zinc}\mathrm{hydrochloric}\mathrm{acid}\mathrm{zinc}\mathrm{chloride}\mathrm{hydrogen}\mathrm{gas}}{\mathrm{Zn}\left(\mathrm{s}\right)+2\mathrm{HCl}\left(\mathrm{g}\right)\to {\mathrm{ZnCl}}_2\left(\mathrm{s}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)}$

Hence, Option (B) is the correct answer.