Activity coefficients quantify the deviation of a real solution's behavior from an ideal solution, where interactions between molecules are non-ideal. They are crucial for accurately predicting concentrations and chemical potentials in various thermodynamic calculations, especially in solutions with strong intermolecular forces or high concentrations.

Activity Coefficients

Activity coefficients

Deviations of a real solution's behavior

An ideal solution is a homogeneous mixture of substances that obeys Raoult's Law, where the interactions between unlike molecules are similar to those between like molecules. This results in a linear relationship between the partial vapor pressure of each component and its mole fraction in the solution, leading to no enthalpy change upon mixing.

ideal solution

interactions between molecules

Non-ideal solutions deviate from Raoult's law due to interactions between different molecules that are not identical to those in the pure components, leading to changes in vapor pressure. These deviations are caused by differences in intermolecular forces such as hydrogen bonding, dipole-dipole interactions, or Van der Waals forces, resulting in either positive or negative deviations from ideal behavior.

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