Calculating Standard Cell Potential
This video presents the same text shown beside it, spoken and on screen. It adds nothing the text does not say.
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.
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.
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.