What does the rate of chemical reactions depend on?

The rate of chemical reactions depends on the temperature, concentration of the reactants, size of the particles reacting and whether there are any catalysts present.

When the temperature is increased, the average kinetic energy of the particles present is increased. When the particles have higher kinetic energy, they move faster and are therefore more likely to collide. The increased temperature also leads to more particles having sufficient energy to react.

When the concentration of reactants is increased, there are more collisions as there are more particles in close proximity to each other.

Collisions (reactions) occur at the surface of particles. The smaller the particle size, the more surface area there is. Because there is more surface area, the reaction will take place more quickly.

Catalysts provide an alternate reaction pathway with a lower activation energy than otherwise required. This means that particles do not need as much energy to react when they collide and therefore increases the rate of the reaction.