Thermodynamic Equilibrium Constant
The dimensionless equilibrium constant defined using activities rather than concentrations or pressures.
Formula / equation
K° = Π a_i^ν
Unit
Dimensionless
In depth
Because each activity is a ratio to a standard state, the thermodynamic constant is genuinely dimensionless and can legitimately appear inside a logarithm in ΔG° = −RT ln K. In dilute ideal solutions activities approach concentrations, so K° and Kc converge numerically.
Examples in the real world
Rigorous calculation of ΔG° from an equilibrium measurement requires activities, not raw molarities.