Heat of transformation at constant pressure and temperature

However, as the generalized Gibbs energy is a function of state, we have, according to relation [1.19]  

By integrating this expression for the whole of the transformation, we obtain  

by using the S5rmmetry of the characteristic matrix Qp =TY,ykSk + Y,v, l, 

the heat of transformation, at constant temperature and pressure, is equal to the enthalpy associated with the reaction. 

Note 1.3.- For a long time, chemists counted the heat released by an exothermic reaction positively. With this old convention, relation [ 1.66] was transformed into  

---