Suppose a reaction A + B --> C occurs at some initial rate at 25°C. Which response includes all of the changes below that could increase the rate of this reaction?

Question

Suppose a reaction A + B --> C occurs at some initial rate at 25°C. Which response includes all of the changes below that could increase the rate of this reaction?

I. lowering the temperature

II. adding a catalyst

III. increasing the initial concentration of B.

The answer is II and III, but can someone please explain why it is II and III and why it is not I?

Answer 1

Generally, lowering the temperature will decrease the rate of the reaction because it decreases kinetic energy of the molecules, thus reducing the number of collisions per unit time.

Adding a catalyst will always increase the rate of a reaction because it provides an alternate path which has a lower activation energy than the normal path.

Increasing the concentration of a reactant will increase the rate of the reaction if, and only if the reaction is not zero order with respect to that reactant. This is because the higher the concentration the more molecules there are per unit volume and hence the greater the chances of collisions.