Step 3: Determine the amount of energy change in the reaction. a) Use the table of enthalpy values (Table A) provided in the Student Worksheet to locate the enthalpy of formation (∆Hf) for each reactant and each product. Record these values along with the reactants and products in Table B of the Student Worksheet. b) Determine the total enthalpy of the reactants and the total enthalpy of the products. Record these values in Table C of the Student Worksheet. c) Use the following formula to find the net change in enthalpy for the reaction and to determine whether the reaction is endothermic or exothermic.