For 10 points, name this measure of deviation from ideality, a factor that is multiplied by concentration.
This quantity can be empirically measured by the mean salt method, which relies on the MacInnes assumption and computes it for a substance as the geometric mean of this quantity for its components. In one model, this quantity is exponential in the excess Gibbs function; that model is the Margules model, which extends the (*) Gibbs-Duhem equation. The difference between the standard and actual chemical potentials is proportional to its logarithm. In dilute solutions of electrolytes, this quantity can be computed to be proportional to the square root of ionic strength, according to the Debye-Huckel equation. It is equal to one in mixtures that obey Raoult's law. For 10 points, name this measure of deviation from ideality, a factor that is multiplied by concentration.
This quantity can be empirically measured by the mean salt method, which relies on the MacInnes assumption and computes it for a substance as the geometric mean of this quantity for its components.
activity coefficient [do accept just activity because it only differs from the coefficient by a trivial factor]