Question

(a) What is a chemical reaction.

(b) State the condition necessary for a chemical change or a reaction to take place.

Answer 1

(a) Chemical reaction - A reaction in which one or more substances undergo a chemical change with the liberation or absorption of energy to form one or more new substances, which is collectively known as chemical change.

Example - When acid and base react with each other it forms salt and water.$$\begin{gathered} \mathrm{NaOH}\left(\mathrm{s}\right)+\mathrm{HCl}(\mathrm{aq}.)\to \mathrm{NaCl}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Sodium}\mathrm{hydroxide}\mathrm{Hyrochloric}\mathrm{acid}\mathrm{Sodium}\mathrm{chloride}\mathrm{Water} \end{gathered}$$

(b) Condition necessary for a chemical change -

• A chemical change occurs when the collision of particles takes place.
• The collision occurs when reactants are in close contact with energy.
• One or more conditions are necessary for a chemical reaction to take place.

1. Mixing - In some cases chemical reactions take place when two substances are mixed with each other.
2. Solution - In some cases chemical reactions take place when two solutions are mixed with each other.