hess' law and enthalpy cycles

• Enthalpy cycle


  A diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess's law
• Hess' law states if a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route
• when drawing enthalpy change of formation cycle, arrows go up
• When drawing enthalpy change of combustion cycle, arrows go down
• enthalpy changes of formation = ΔfH of products - ΔfH of reactants
• enthalpy changes of combustion = ΔcH of reactants - ΔcH of products