For the gas-phase reaction
1. The true (dimensionless) equilibrium constant
where ai is the activity of species i
where fi = fugacity of species i
= fugacity of species i at the standard state. For gases, the standard state is 1 bar, which is in the noise level of 1 atm, so we will use atm.
where γi is the activity coefficient
K = True equilibrium constantKy = Activity equilibrium constantKp = Pressure equilibrium constantKc = Concentration equilibrium constant
Kγ has units of