Heat of Formation and Heat of Reaction

Standard enthalpies of reactions are calculated by using the principle expressed by Eq. (7.1) and thermodynamic tables of standard heats of formation. The heat of formation (flH1)1 for all is calculated from the heats of reaction for the species formed from its elements. For the reaction stoichiometry of species formed from its elements

£J,e is the stoichiometric coefficient of the eth element in the formation of the jth species and (llH1) 1 is the heat of formal ion (like the heat of reaction) associated with the formation of species Equation l) can be derived multiplying both sides of Eq. (7.6) by a1 and summing over j = 1, ... , S (Aris, 1966):

s y s s y s

The second term of Eq. (7.7) vanishes, because the reaction is balanced [Eq. (5. in each elementary species and the following equality holds for all e elements:

Using Eq. (7.8), Eq. (7.7) becomes s s

Using Eq. in Eq. (7.9) it can be seen that the heat of reaction can be calculated from the heat of formation of each involved in a reaction:

s

t::.H = LaJ{t::.H1)1 j=!