A galvanic cell is built from one half cell of standard reduction potential minus 0.76 V and another of plus 0.34 V. What is the standard emf of the cell?

1. The emf of a cell is the maximum potential difference between its two half cells. 2. Both listed values are reduction potentials, but only one half cell can actually be reduced. 3. The half cell with the more positive value is reduced, so it is the cathode. 4. That is the half cell at plus 0.34 volts. 5. The other half cell is oxidised, so it is the anode, and that is the one at minus 0.76 volts. 6. The emf is the value at the cathode minus the value at the anode. 7. That is 0.34 volts minus minus 0.76 volts, which is 0.34 plus 0.76, giving 1.10 volts. 8. The 0.42 volt answer is the trap for adding the two values as written instead of subtracting a negative, while 0.34 volts and 0.76 volts each quote a single half cell and forget that emf is a difference. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 13: Electrochemical reactions_