Standard potential for intermediate (coupled) half-cell

Rarely Tested

Using Ξ”GΒ°=βˆ’nF EΒ° (GΒ° additive), for:

  • $$\Delta G^\circ_{M^{n+}/M}=-nF\,E^\circ_{M^{n+}/M},$$
  • $$\Delta G^\circ_{M^{m+}/M}=-mF\,E^\circ_{M^{m+}/M}.$$

Reverse the second reaction (oxidation) to add +mF EΒ°; summing gives:

$$-nF\,E^\circ_{M^{n+}/M}+mF\,E^\circ_{M^{m+}/M}=-(n-m)F\,E^\circ_{M^{n+}/M^{m+}}$$
Thus:
$$E^\circ_{M^{n+}/M^{m+}}=\frac{n\,E^\circ_{M^{n+}/M}-m\,E^\circ_{M^{m+}/M}}{\,n-m\,}$$

For the half-reaction: $$M^{n+}+(n-m)e^-\rightarrow M^{m+}.$$

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