Any @O04362@-reduction (redox) reaction can be divided into two half reactions: one in which a chemical species undergoes @O04362@ and one in which another chemical species undergoes reduction. If a half- reaction is written as a reduction, the driving force is the reduction potential. If the half-reaction is written as @O04362@, the driving force is the @O04362@ potential related to the reduction potential by a sign change. So the redox potential is the reduction/@O04362@ potential of a compound measured under standards conditions against a standard reference half-cell. In biological systems the standard redox potential is defined at pH – 7.0 versus the hydrogen electrode and @P04420@ of hydrogen = 1 @B00596@.