Calculation of equilibrium using fugacities

[Notwen7]

Its been a while since I took thermo. I was looking through my notes regarding fugacity at chemical equilibrium. There was a clever algorithm used to determine whether the pure compound was at equilibrium based upon the varying pressure with a constant temperature. It had the calculation "(fL/fv)-1" display values, fL being fugacity of the liquid and fv being the fugacity of the vapor. After several inputs of different pressures this calculation will approach 0. Now if "(fL/fv)-1" equals zero then fugacities are equal yielding a chemical equilibrium.

Now if my memory serves there is a reason why we use "(fL/fv)-1" in lieu of "(fv/fL)-1". I am not sure why fL has to be in the numerator. If someone can assist me or show me the right direction I would greatly appreciate it.

 

[danago]

When the system is in vapour-liquid equilibrium, the fugacity of the vapour will be equal to the fugacity of the liquid, so it should not matter which fugacity is the numerator.

http://en.wikipedia.org/wiki/Vapor–...namic_description_of_vapor-liquid_equilibrium