Activity Coefficient

Chemical Thermodynamics

Depending on a specific area of fundamental science and technology, the term “activity” may have a different meaning. For example, in chemical thermodynamics, activity (a) is well known as a convenient variable to represent data, obtained experimentally or calculated theoretically, for the values of chemical potentials of components in real chemical solutions. For the $i-th$ component of a mixture, activity a _i is defined as follows: ${\mu}_i={\mu}_i^0+RT \ln \left({a}_i\right)$, where μ _i is the chemical potential of a component and μ ⁰ _i is the chemical potential of that component in standard state. R is the gas constant and T is the thermodynamic temperature. The numerical value of the activity depends on the choice of a standard state, as it describes the difference between an actual chemical potential and a standard chemical potential.

Fuel Cells and Electrocatalysis

In hydrogen fuel cell science and technology, activity is often referred to as the...