Why is the rate of reaction slow at low temperatures?
Because the reactant particles collide less frequently, and are less likely to react when they do collide.
Collusion Theory tells us for a reaction to happen the reactants gave to collide with each other, and they have to collide with energy greater than the Activation Energy for the reaction.
When we do a reaction at a lower temperature, the reacting particles have less kinetic energy (particles move faster the hotter they are),
As a result they collide with each other less frequently. In addition, when they do collide they are less likely to have energy greater than the Activation Energy, so each collision is less likely to be successful. As a result, the reaction happens at a slower rate.