Question

Which expression represents the ΔH for a chemical reaction in terms of the potential energy, PE, of its products and reactants?

Answer 1

2 - PE of products-PE of reactants.

You are trying to calculate the energy change that occurred from the start of the reaction (the reactants going in) to the end of the reaction (the products coming out). Therefore if there is more energy at the end, you will get a positive result from subtracting the PE of the reactants, and vice versa.