3.2.13 (HL)—Standard cell potential (E⦵cell)

A positive E°cell indicates a spontaneous voltaic direction. Reverse the direction if the calculated sign is negative.

Select the more positive reduction potential as the cathode reaction, keep both tabulated values as reduction potentials, and calculate E°cell = E°cathode − E°anode. Do not multiply an electrode potential when a half-equation is scaled.

Worked $E^\circ_{cell}$ example: $E^\circ(\ce{Ag+/Ag})=+0.80\,\mathrm{V}$ and $E^\circ(\ce{Cu^{2+}/Cu})=+0.34\,\mathrm{V}$. Silver is the cathode, so $E^\circ_{cell}=E^\circ_{cathode}-E^\circ_{anode}=0.80-0.34=+0.46\,\mathrm{V}$. The positive result predicts the spontaneous reaction $\ce{2Ag+ + Cu -> 2Ag + Cu^{2+}}$ under standard conditions. Do not multiply $E^\circ$ when doubling the silver half-equation.