Answer: Change in chemical composition of reactants is an event which must always occur for a chemical reaction to take place.
Explanation:
A chemical reaction is defined as a reaction in which there will always occur change in chemical composition of reactant species.
For example, [tex]AgNO_{3} + HCl \rightarrow AgCl + HNO_{3}[/tex]
Here, chemical composition of both [tex]AgNO_{3}[/tex] and HCl changes which leads to the formation of silver chloride and nitric acid. Hence, it is a chemical reaction.
Therefore, we can conclude that change in chemical composition of reactants is an event which must always occur for a chemical reaction to take place.
