Question

3 (b). Discuss at least two chemical reactions in which gas is evolved.

Answer 1

• A chemical reaction may take place when two or more reactants come in contact with one another resulting in the formation of new substances called products accompanied by the transfer of energy among them.
• Certain chemical reactions are characterized by the evolution of a gas.

Examples:

• When Zinc metal is treated with dilute sulfuric acid, hydrogen gas is evolved. The hydrogen gas burns with a pop sound.
• $\underset{\mathrm{Zinc}\mathrm{Sulfuric}\mathrm{acid}\mathrm{Zinc}\mathrm{sulfate}\mathrm{Hydrogen}}{\mathrm{Zn}+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{dil}\right)\to {\mathrm{ZnSO}}_4+{\mathrm{H}}_2}$
• 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.
• $\underset{}{\underset{\mathrm{Sodium}\mathrm{carbonate}}{{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrohloric}\mathrm{acid}}{2\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Sodium}\mathrm{chloride}}{2\mathrm{NaCl}\left(\mathrm{aq}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}}$