Question

How is the energy level of the products affected by the presence of a catalyst?

Answer 1

A reaction needs a certain amount of energy, called the activation energy, for its reactants to form products.

When a catalyst is added, it provides an alternative pathway for the reactants to form products by lowering the activation energy.

So the products are formed with a lower activation energy.  

This does not affect the energy of the products however, as seen in the diagram below for an exothermic reaction.

(energy of products < energy of reactants)

Or an endothermic reaction  

(energy of products > energy of reactants)