Activity coefficient

Activity Coefficient

The activity coefficient is a dimensionless quantity in physical chemistry and thermodynamics that represents the deviation of a mixture from ideal behavior. It is a measure of the excess or deficit in the chemical potential of a component in a mixture as compared to the chemical potential of the same component in a standard state.

Definition

The activity coefficient, denoted by γ, is defined as the ratio of the activity, a, of a substance to its molar concentration, c. The activity of a substance is a measure of its 'effective concentration' in a mixture, taking into account interactions with other components of the mixture.

<math>\gamma = \frac{a}{c}</math>

Determination

The activity coefficient can be determined experimentally by measuring properties of the mixture such as vapor pressure, osmotic pressure, or electrolytic conductivity, and comparing these to the properties of an ideal mixture.

Applications

Activity coefficients are used in various fields of science and engineering, including chemical engineering, environmental science, and pharmaceutical science. They are particularly important in the design of chemical reactors, the prediction of solubility of solids in liquids, and the calculation of phase equilibrium in multicomponent systems.

See also

• Chemical potential
• Thermodynamics
• Physical chemistry
• Chemical engineering
• Environmental science
• Pharmaceutical science

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