https://doi.org/10.1351/goldbook.A00116
The activity
coefficient
fB of a substance B in a liquid or solid mixture containing
mole
fractions xB, xC, ... of the substances B, C, ... is a dimensionless quantity defined in terms of the
chemical potential
μB of B in the mixture by: R T ln(xB fB)=μB(cd,T,P,x)μB(cd,T,p) where x denotes the set of
mole
fractions xB, xC, ... . The activity
coefficient
γB of a solute B in a solution (especially a dilute liquid solution) containing molalities mB, mC, ... of solutes B, C, ... in a solvent A is a dimensionless quantity defined in terms of the
chemical potential
μB by: R T ln(mB γBm)=μB{μBR T ln(mBm)}
Sources:
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2171 [Terms] [Paper]
PAC, 1994, 66, 533. (Standard quantities in chemical thermodynamics. Fugacities, activities and equilibrium constants for pure and mixed phases (IUPAC Recommendations 1994)) on page 543 [Terms] [Paper]
PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 960 [Terms] [Paper]