1. When the system at constant pressure undergoes changes from an initial state with H1, U1, V1 and P parameters to a final state with H2 , U2 , V2 and P parameters, the change in enthalpy ∆H, is given by ∆H = U + PV
qp is the heat absorbed at constant pressure and is considered as heat content.
3. Consider a closed system of gases which are chemically reacting to produce product gases at constant temperature and pressure with V. and as the total volumes of the reactant and product gases respectively, and n1 and nf are the number of moles of gaseous reactants and products.
Then,
