Explain how a catalyst can effect the rate of a forward and reverse reaction.

A catalyst can provide a different mechanism or pathway for a chemical reaction through stabalistion of the transition state. The catalyst will lower the activation energy of the reaction meaning a greater number of molecules will have sufficient energy to react at any one time. A catalyst will increase the rate of both the forward and the reverse reaction.
The activation energy refers to the minimum energy required for a reacting species to undergo a transformation.