The thermodynamic definition of the equilibrium constant is

where Δ_{r }*G** ^{o}* is the reaction Gibbs energy at standard conditions (a constant for a particular reaction),

*R*is the gas constant,

*T*is temperature.

Since logarithms only take pure numbers, *K* is a dimensionless number. However, when equilibrium constants are calculated as a quotient of concentrations or partial pressures,

the practice is to quote them in units of concentration or pressure according to the quotient, for example, the units of *K _{c}* for

is mol* ^{-4}*dm

*.*

^{12}

##### Next article: The relationship between K_{p} and K_{c}

_{p}

_{c}