Cell EMF from electrode potentials
Ecell = E(reduction at positive electrode) - E(reduction at negative electrode)
Keep both values as reduction potentials: more positive minus more negative.
Work it, then mark it
Do each calculation on paper first, then reveal the mark scheme and tick the marks you actually earned — the same way you should mark past papers.
E(Cu2+/Cu) = +0.34 V and E(Zn2+/Zn) = -0.76 V. Calculate the standard EMF and state the spontaneous reaction direction.
Do the calculation on paper first — then mark it.
Where the marks get lost
- Adding a negative potential without brackets.
- Reversing a half-equation and also changing the tabulated E value's sign.
Exam tip: Tabulated values stay as reduction potentials; subtract the less positive value from the more positive value.
Calculations are the most trainable marks in chemistry
They come up every paper and reward a clean method. Send me one you keep dropping marks on — your first lesson is free.