Explain why increasing the concentration of a reactant in solution increases the rate of a chemical reaction, with reference to collision theory and activation energy.

Increasing the concentration of a reactant raises the number of solute particles per unit volume. A higher particle density means that, on average, a given volume of solution contains more reactant molecules or ions, so the frequency of collisions between reactant particles increases.

According to collision theory, only collisions that have sufficient energy (≥ Eₐ) and the correct orientation lead to product formation. The proportion of collisions that meet these criteria is independent of concentration; however, because there are more collisions overall, the absolute number of collisions that possess energy equal to or greater than the activation energy rises.

Consequently, the number of successful collisions per unit time increases, which directly raises the rate of the chemical reaction.