Since enthalpy is an extensive property, the quantity of heat obtained from a reaction will depend on the amounts of reactants.  The same methods used to solve stoichiometry problems can be used with thermochemical equations.  Essentially  what we do is to treat the quantity of heat as if it were a quantity of a reactant or product. Consider the following example.

What is the enthalpy change associated with the formation of 95.6 g of HCl(g) in the reaction?

H₂(g) + Cl₂(g) ==> HCl(g) H = -184.6 kJ

Solution