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Electrons in solids have a chemical potential, defined the same way as the chemical potential of a chemical species: The change in free energy when electrons are added or removed from the system. In the case of electrons, the chemical potential is usually expressed in energy per particle rather than energy per mole, and the energy per particle ...
The relative activity of a species i, denoted a i, is defined [4] [5] as: = where μ i is the (molar) chemical potential of the species i under the conditions of interest, μ o i is the (molar) chemical potential of that species under some defined set of standard conditions, R is the gas constant, T is the thermodynamic temperature and e is the exponential constant.
μ i is the electrochemical potential of species i, in J/mol, μ i is the chemical potential of the species i, in J/mol, z i is the valency (charge) of the ion i, a dimensionless integer, F is the Faraday constant, in C/mol, Φ is the local electrostatic potential in V. In the special case of an uncharged atom, z i = 0, and so μ i = μ i.
where ρ si is the partial density of the i th species. Beyond this, in chemical systems other than ideal solutions or mixtures, the driving force for the diffusion of each species is the gradient of chemical potential of this species. Then Fick's first law (one-dimensional case) can be written
Effective concentration (activity) 1 mol/L for each aqueous or amalgamated (mercury-alloyed) species; Unit activity for each solvent and pure solid or liquid species; and Absolute partial pressure 101.325 kPa (1.00000 atm; 1.01325 bar) for each gaseous reagent — the convention in most literature data but not the current standard state (100 kPa).
z i the charge per ion of the species i; F, Faraday constant (the electrochemical potential is implicitly measured on a per-mole basis) φ, the local electric potential. Sometimes, the term "electrochemical potential" is abused to describe the electric potential generated by an ionic concentration gradient; that is, φ.
When the formal potential is measured under standard conditions (i.e. the activity of each dissolved species is 1 mol/L, T = 298.15 K = 25 °C = 77 °F, P gas = 1 bar) it becomes de facto a standard potential. [5]
In thermodynamics, the excess chemical potential is defined as the difference between the chemical potential of a given species and that of an ideal gas under the same conditions (in particular, at the same pressure, temperature, and composition). [1] The chemical potential of a particle species is therefore given by an ideal part and an excess ...