Editing Redox (section)

==Standard electrode potentials (reduction potentials)==
Each half-reaction has a standard [[electrode potential]] (''E''{{su|p=o|b=cell}}), which is equal to the potential difference or [[voltage]] at equilibrium under [[standard state|standard conditions]] of an [[electrochemical cell]] in which the [[cathode]] reaction is the [[half-reaction]] considered, and the [[anode]] is a [[standard hydrogen electrode]] where hydrogen is oxidized:<ref>{{Cite book |title=Chemistry: the central science |date=2015 |publisher=Pearson |isbn=978-0-321-91041-7 |editor-last=Brown |editor-first=Theodore L. |edition=13 |location=Boston, Mass. |pages=Chapter 4}}</ref>
:{{1/2}}H<sub>2</sub> → H<sup>+</sup> + e<sup>−</sup>

The electrode potential of each half-reaction is also known as its reduction potential (''E''{{su|p=o|b=red}}), or potential when the half-reaction takes place at a cathode. The reduction potential is a measure of the tendency of the oxidizing agent to be reduced. Its value is zero for H<sup>+</sup> + e<sup>−</sup> → {{1/2}}H<sub>2</sub> by definition, positive for oxidizing agents stronger than H<sup>+</sup> (e.g., +2.866 V for F<sub>2</sub>) and negative for oxidizing agents that are weaker than H<sup>+</sup> (e.g., −0.763V for Zn<sup>2+</sup>).<ref name="Petrucci2017" />{{rp|873}}

For a redox reaction that takes place in a cell, the potential difference is:
:''E''{{su|p=o|b=cell}} = ''E''{{su|p=o|b=cathode}} − ''E''{{su|p=o|b=anode}}

However, the potential of the reaction at the anode is sometimes expressed as an ''oxidation potential'':
:''E''{{su|p=o|b=ox}} = −''E''{{su|p=o|b=red}}
The oxidation potential is a measure of the tendency of the reducing agent to be oxidized but does not represent the physical potential at an electrode. With this notation, the cell voltage equation is written with a plus sign
:''E''{{su|p=o|b=cell}} = ''E''{{su|p=o|b=red(cathode)}} + ''E''{{su|p=o|b=ox(anode)}}