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Basic Thermodynamic Principles

Fugacity and Fugacity Coefficient

Fugacity can be thought of as the corrected partial pressure (\(p_i=u_i\cdot p\) where \(u_i\) is either \(z_i\), \(x_i\) or \(y_i\)) of a component in a mixture where the fugacity coefficient is the correction term to the partial pressure for non-ideal conditions. Based on this description, you would expect the fugacity coefficient (\(\phi_i\)) to tend to 1 as the fluid acts ideal, as is the case.


Chemical Potential

Gibbs Free Energy

where \(u_i\) can be either the liquid molar composition (\(x_i\)) or the vapor molar composition (\(y_i\)).

Thermodynamic Equilibrium

Equal Chemical Potential Criteria

Equal Fugacity Criteria