Chapter 15. Yang–Yang Critical Anomaly

Isochoric heat capacity, cV, is a thermodynamic property of fluids and fluid mixtures with a variety of scientific applications. cV is distinctly different from the commonly measured isobaric heat capacity, cP, which is often used by engineers in process design calculations. On the one hand, cV and cP show similar behaviors as a function of temperature and pressure in the singlephase (liquid or vapor) region. On the other hand, only cV is measurable inside the vaporþ liquid coexistence region, while cP is not a measurable property. In terms of a process explanation, with a pure substance in a calorimeter when P is held constant in the vaporþ liquid coexistence region, then energy added by heating (DH) serves solely to evaporate liquid to the vapor phase without increasing the temperature of the sample (DT1⁄4 0); thus, the apparent heat capacityE(DH/DT)p would have an indeterminant value. In this study, we will take advantage of cV measurements that are made inside, outside and on the boundary of the vaporþ liquid coexistence region. Careful measurements of