Question

E. Tick the most appropriate answer:

5. During a chemical change :

• A. state of substance changes only
• B. composition of a substance changes only
• C. both state as well as composition of substance change
• D. none of these

Answer 1

The correct option is C

both state as well as composition of substance change

The following are some features of a chemical change:

• A chemical change is permanent in nature.
• One or more new substances are formed as the original composition of the matter changes. For example, hydrochloric acid reacts with sodium hydroxide solution to form sodium chloride (salt) and water with the evolution of a lot of heat.

$\underset{\mathrm{Sodium}\mathrm{Hydroxide}}{\mathrm{NaOH}\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Sodium}\mathrm{Chloride}}{\mathrm{NaCl}\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\mathrm{heat}\mathrm{energy}$

• In a chemical change, energy can be emitted or received in the form of heat, light, or electricity.
• Certain chemical reactions are characterized by a change in state.
• For example, two volumes of hydrogen gas react with one volume of oxygen gas to form water which is in a liquid state.
• $\underset{\mathrm{Hydrogen}\mathrm{gas}}{2{\mathrm{H}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Oxygen}\mathrm{gas}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

Hence, Option (C) is the correct answer.