Editing Electrochemical potential (section)

== Uses ==

Differences in electrochemical potential are measurable and physically meaningful:<ref name="guggeinheim-book"/>
* If two bodies have equal temperatures but differ in electrochemical potential of some species, then that species will spontaneously move from higher to lower electrochemical potential if able.
* At equilibrium, electrochemical potentials for each species will equalize throughout the domain that it can travel. For example, the  <math>\bar \mu</math> of any ion will equalize across a semi-permeable membrane that permits that ion to pass through, while impassable ions will not equalize their <math>\bar \mu</math>.
* Two disconnected bodies of exactly identical compositions may have a difference <math>\Delta \phi</math> in electrostatic potential. The electrochemical potential differences <math>\Delta\bar\mu_i</math> between the two bodies is then given by:
::<math>\Delta\bar\mu_i = z_i F \Delta \phi.</math>
* Equilibrium chemical reactions are expressible as an equality (zero difference) in electrochemical potentials, e.g. the [[hydrogen electrode]] reaction <chem display="inline">2H_{(aq)}+ + 2e- <=> H2_{(g)}</chem> requires at equilibrium that <math>2\bar\mu_{\mathrm H^+} + 2\bar\mu_{\mathrm e^-} = \bar\mu_{\mathrm H_2}</math>.
* Differences in the electron electrochemical potential <math>\bar\mu_{\mathrm e^-}</math> are precisely what is measured by DC voltmeters. The electron electrochemical potential is also known as the [[Fermi level]] of solid-state physics.