Thermodynamic Quantities for Pure Liquids and Solids

With the above quantities, aU the thermodynamics of real gases can be described, once the real gas parameters, such as the van der Waals constants or the virial coefficients, are known. 

For pure solids and liquids, jointly called condensed phases, the volume is determined by the molecular size and molecular forces it does not change much with changes in p and T. Since the molecular size and forces are very specific to a compound, there is no generally valid equation of state. A relation between V, T and p is expressed in terms of the coefficient of thermal expansion a and the isothermal compressibility Kj defined by (5.4.5) and (5.4.6). If we consider Fas a function of p and T, V(p, T), we can write 

The values of a and Kj are small for solids and liquids. For liquids the coefficient of thermal expansion a is in the range 10 to 10 and the isothermal compressibility Kj is about 10 atm Solids have a in the range 10 to 10 K and Kj in the range 10 to 10 atm . Table 6.1 lists the values of a and Kj for some liquids and solids. Furthermore, the values of a and Kj are almost constant for temperature variations of about 100 K and pressure variations of about 50 atm. Therefore (6.3.1) can be integrated to obtain the following equation of state  

Thermodynamically, the characteristic feature of solids and liquids is that i, S, and H change very little with pressure, hence they are essentially functions of T for a given N. If entropy is considered as a function of p and T, then 

75JK mol Though Cp approaches zero, so S is finite as T —0, the molar entropy of water atp = 1 atm and T = 298 K is about 70 Thus, it is clear that the third term in (6.3.6) that contains p is insignificant compared to the second term. Since this is generally true for solids and liquids, we may write 

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