Isopiestic Systems. The Heat-Content Function

Isentropic-isopiestic systems. The heat-content function. 

For equilibrium therefore (dw)s p must be zero or negative, and ms.,+pms., o is the condition for equilibrium. 

For any finite change of state carried out reversibly at constant entropy and pressure, we have 

Isentropic-isopiestic systems are of no great practical importance, and the chief value of the function H lies in its relationship to the heat of reaction at constant pressure, Qp, Suppose that we allow a chemical system to react at the atmospheric pressure, in such a manner that the only work don-e is that due to the change in the volume of the system. 

The heat of reaction at constant pressure is therefore equal to the change in the function H. For this reason H is called the heat content of the system, or the heat function for constant pressure. 

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