An Oxidation-reduction or redox reaction involves the transfer of electrons from the reducing agent to the oxidizing agent. Species that undergo an increase in their oxidation state are oxidized, while those that experience a decrease in their oxidation state are reduced. So, the thermodynamics of the redox reaction is expressed in terms of the moving electron. The free energy change for a redox reaction is –nFE, where n is the number of electrons, F is Faraday's constant, and E is the electrochemical potential. However, the Gibbs free energy of a reaction is a function of the concentrations of the reactants and products. Substituting for ΔG in this equation gives the relationship with the electrochemical potential, and dividing by –nF results in the Nernst equation. As ΔG is zero at equilibrium, E must be zero, so the reaction quotient equals the equilibrium constant. Considering the values of constants at 25°C and expressing the Nernst equation using base-ten logarithms gives the relation between the standard state potential and the equilibrium constant.