Fugacity capacity constant

Fugacity has units of pressure, and can be related to the concentration of a chemical in a system through a fugacity capacity constant, commonly with units of (mol/atm m3). Thus the chemical concentration in a given... 

The fugacity was defined above in terms of a concentration and a fugacity capacity. At constant pressure and temperature, fugacity capacities were constant (except when isotherms were nonlinear). Hence, Eq. (55) can be simplified to the following ... 

The fugacity capacity for other phases is a function of both the chemical s partition coefficient between that phase and water and the chemical s Henry s law constant. For water, the fugacity capacity is... 

The equilibrium constant is then the ratio of the fugacity capacities. The magnitude of Z will depend on temperature and the properties of the compound as they relate to the characteristics of a given phase. Compounds will accumulate in compartments with a high value of Z. The next step is to define Z for environmental compartments air, water, soil, sediments, and biota. 

The fugacity capacity in water is thus the reciprocal of the Henry s law constant. It should be emphasized that the concentration of the compound in water refers only to the amount in solution and does not include compound that could be associated with suspended sediment, for example. 

Figure 5.17 illustrates the effect on hydrate formation when ethane and propane are combined at constant temperature. Ethane acts as an inhibitor to sll formation due to competition of ethane with propane to occupy the large cages of sll. Propane also acts as an inhibitor to si formation when added to ethane+water. In this case, however, since propane cannot enter the si cavities, the fugacity of ethane is lowered as propane is added, destabilizing the si hydrate. Holder (1976) refers to this inhibiting capacity as the antifreeze effect. 

The graphs are based on the Peng-Robinson equation of state (1) as improved by Stryjek and Vera (2, 3). The equations for thermodynamic properties using the Peng-Robinson equation of state are given in the appendix for volume, compressibility factor, fugacity coefficient, residual enthalpy, and residual entropy. Critical constants and ideal gas heat capacities for use in the equations are from the data compilations of DIPPR (8) and Yaws (28, 29, 30). 

Cp Heat capacity at constant pressure /, Fugacity of pure component i... 

Since the heat capacities in the ideal gas state are usually better known than the heat capacities of the liquids or the solids, even for reactions in the liquid phase it is often advantageous to use the values for the ideal gas for the determination of the equilibrium constant. This choice has no influence on the results, if the correct value of the standard fugacity/j° (1 atm instead of Pi ) is used for the calculation of the equilibrium conversion. 

NIST/ASME Steam Properties Database versiou 2.21 http //www.nist.gov/srd/nistlO.cfm (accessed November 10, 2010) (purchase required). Thermophysical properties include in the STEAM Database temperature, Helmholtz energy, thermodynamic derivatives, pressure, Gibbs energy, density, fugacity, thermal conductivity, volume, isothermal compressibility, viscosity, dielectric constant, enthalpy, volume expansivity, dielectric derivatives, internal energy, speed of sound, Debye-Hlickel slopes, entropy, Joule-Thomson coefficient, refractive index, heat capacity, surface tension. The STEAM database generates tables and plots of property values. Vapor-liquid-solid saturation calculations with either temperature or pressure specified are available. 

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