Question

3 (b) By giving at least two examples describe the evolution of gas in a chemical reaction.

Answer 1

• The process by which substances join or break apart chemically is called a chemical reaction.
• Evolution of gas: Certain chemical reactions are characterized by the evolution of a gas.

The following examples will prove the point.

• When dilute hydrochloric acid reacts with sodium carbonate, then sodium chloride, carbon dioxide, and water are formed. A brisk effervescence is seen in the evolution of carbon dioxide.

$\underset{}{\underset{\mathrm{Sodium}\mathrm{carbonate}}{{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrohloric}\mathrm{acid}}{2\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Sodium}\mathrm{chloride}}{2\mathrm{NaCl}\left(\mathrm{aq}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}}$

• When Zinc metal is treated with dilute sulfuric acid, hydrogen gas is evolved. The hydrogen gas burns with a pop sound.

$\underset{\mathrm{Zinc}\mathrm{Sulfuric}\mathrm{acid}\mathrm{Zinc}\mathrm{sulfate}\mathrm{Hydrogen}}{\mathrm{Zn}+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{dil}\right)\to {\mathrm{ZnSO}}_4+{\mathrm{H}}_2}$