From the First Law of Thermodynamics, it can be shown that the enthalpy of a reaction can be determined from the heats of formation for reactants and products: ΔHrxn = ΣΔHf(products) - ΣΔHf(reactants)
This page presents "generic" problems to provide practice in applying the above relationship. The problems are generic in that basic symbols are used to represent the chemical species rather that using actual chemical formulas. Further, to emphasize the methodology rather than the numbers, all heats of formation will have one sign figure and be between 10 and 100. When you press new problem, a "balanced chemical equation" and a table of heats of formation will be presented. Calculate the heat of the reaction, enter it in the answer cell and press "Check Answer." Pressing "Show Answer" will display a complete solution.