Free enthalpy fugacity

All values for the free enthalpy of formation are as a rule standardised for the ideal gaseous state of 1 (bar), (Standard State this ideal state is called fugacity). This also holds for the group contributions given. 

The product of activity coefficients /and the mole fraction x is often called activity a. It is noteworthy that the chemical equilibrium constant can only be calculated if the acitivity coefficients are known. In the case of reactive distillation, this information is available. It should be mentioned that the equilibrium constant can be calculated from the pure free enthalpies of formation that have to be corrected to the reaction state depending on the model (activity coefficients or fugacity) used. 

That is why the direction of this reaction is determined by values of Oj and H fugacity. As free enthalpy at the formation of given gas components are equal to 0, the moisture formation equilibrium constant of them is determined by free enthalpy of H O formation, i.e., log = -0.733-56.69 = - 41.55 (see formula (1.105)). Besides, at low pressure fugacity may be assumed equal to partial pressure. Then... 

The physical property monitors of ASPEN provide very complete flexibility in computing physical properties. Quite often a user may need to compute a property in one area of a process with high accuracy, which is expensive in computer time, and then compromise the accuracy in another area, in order to save computer time. In ASPEN, the user can do this by specifying the method or "property route", as it is called. The property route is the detailed specification of how to calculate one of the ten major properties for a given vapor, liquid, or solid phase of a pure component or mixture. Properties that can be calculated are enthalpy, entropy, free energy, molar volume, equilibrium ratio, fugacity coefficient, viscosity, thermal conductivity, diffusion coefficient, and thermal conductivity. 

It is believed that ASPEN provides a state-of-the-art capability for thermodynamic properties of conventional components. A number of equation-of-state (EOS) models are supplied to handle virtually any mixture over a wide range of temperatures and pressures. The equation-of-state models are programmed to give any subset of the properties of molar density, residual enthalpy, residual free energy, and the fugacity coefficient vector (and temperature derivatives) for a liquid or vapor mixture. The EOS models (named in tribute to the authors of such work) made available in ASPEN are the following ... 

The chemical potential provides the fundamental criteria for determining phase equilibria. Like many thermodynamic functions, there is no absolute value for chemical potential. The Gibbs free energy function is related to both the enthalpy and entropy for which there is no absolute value. Moreover, there are some other undesirable properties of the chemical potential that make it less than suitable for practical calculations of phase equilibria. Thus, G.N. Lewis introduced the concept of fugacity, which can be related to the chemical potential and has a relationship closer to real world intensive properties. With Lewis s definition, there still remains the problem of absolute value for the function. Thus,... 

The quantities AGf° and AHf° refer to free energies and enthalpies of formation from the elements with consumption or production of gaseous electrons if necessary. Standard states of elementary hydrogen and oxygen are one atmosphere fugacity. The standard state of the... 

Determine the equilibrium composition that is achieved at 300 bar and 700 K when the initial mole ratio of hydrogen to carbon monoxide is 2. You may use standard enthalpy and Gibbs free energy of formation data. For purposes of this problem you should not neglect the variation of the standard heat of reaction with temperature. You may assume ideal solution behavior but not ideal gas behavior. You may also use a generalized fugacity coefficient chart based on the principle of corresponding states as well as the heat capacity data listed below. 

For synthesis processes it should be added that basic chemical equilibrium data such as the free energy and enthalpy of formations originally have been derived from experimental data using a specific method to correct for non-ideal gas fugacity coefficients. This must be taken into consideration when selecting an appropriate method. This is the case for methanol, where a generalised method only as a function of... 

---