The amount of energy released or absorbed by a chemical process depends on the amount of reactants undergoing the process. If more of the reactants are used, then the energy change will increase. If less of the reactants are used, then the energy change will decrease. This means that energy calculations are essentially stoichiometry calculations that use the same principles of problem solving used in mass to mass stoichiometry problems. The difference is of course that the you must be aware of the molar heat changes associated with a reaction.