Chemistry / Unit 11 Chem 2174 worked example, 60 to 90 seconds
Calculating Standard Cell Potential
The idea
Calculating a standard cell potential means identifying which tabulated half-reaction serves as the cathode and which as the anode — the one with the more positive reduction potential is the cathode — then subtracting the anode's value from the cathode's: E°cell = E°cathode − E°anode.
In practice
Pairing Cu²⁺ + 2 e⁻ → Cu, E° = +0.34 V, as the cathode against Zn²⁺ + 2 e⁻ → Zn, E° = −0.76 V, as the anode gives E°cell = 0.34 − (−0.76) = 1.10 V, positive and so spontaneous as written, confirming zinc is correctly assigned the anode role since it has the lower reduction potential of the pair.
Where people slip
Reversing a half-reaction to write it as an oxidation and then flipping its tabulated sign before subtracting, rather than subtracting the two reduction values directly, is a common way to double the sign error.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Something wrong in this lesson? Flag it · Sources for Chemistry