Premium
Hypothetical standard states and the thermodynamics of high‐pressure phase equilibria
Author(s) -
Prausnitz J. M.
Publication year - 1960
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690060116
Subject(s) - thermodynamics , chemistry , equation of state , volume (thermodynamics) , thermodynamic equilibrium , phase (matter) , component (thermodynamics) , state function , function (biology) , high pressure , standard deviation , mathematics , statistics , physics , organic chemistry , evolutionary biology , biology
Thermodynamic analysis of phase‐equilibrium data is necessary for testing such data, for extension to new conditions, and for purposes of correlation and prediction of phase‐equilibrium behavior. While such analysis is common for low‐pressure systems, it is rare for high‐pressure systems owing to difficulties encountered in the definition of standard states. For a gaseous solute in the liquid phase it is proposed that the standard state be taken as the hypothetical liquid at the temperature and total pressure of the solution. The properties of this standard state are specified by the temperature and total pressure and by the specific volume which the substance would have if it did not experience a phase change. This standard state is useful since it is not a function of the solution but only of the substance being considered. For a condensable component in the gas phase it is convenient for most purposes to define the standard state as the ideal gas at the temperature and total pressure of the solution, but to separate the effect of composition on the activity coefficient from that of pressure, it is proposed to define the standard state as the real hypothetical gas at the solution conditions. To illustrate these ideas, activity coefficients are computed for several high‐pressure systems, and it is shown how these activity coefficients may be used in the correlation, testing, and extension of high‐pressure phase‐equilibrium data.