# What is fugacity?

1. Apr 25, 2014

### alighazanfer25

What is fugacity ? I know it the corrected pressure for non ideal systems , but I need a much more intuitive sense of the term. It would be nice to get some help on this...

2. Apr 25, 2014

### Simon Bridge

The intuitive sense for it is "pressure" - a pressing in against a surface.
It's basically a way to convert ideal gas equations into equations more useful for real gasses.

3. Apr 26, 2014

### Staff: Mentor

For an ideal gas, VdP = RT d lnP

For a real gas, we use an equation of the same form to express VdP:

VdP = RT d ln f

where f is the fugacity. This is used to determine the change in Gibbs free energy dG = VdP at constant temperature. So dG = RT d ln f. In practice, it is easier to work in terms of the fugacity than the pressure when working in the non-ideal gas region.

Chet