# 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.

where

## 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