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For the cell represented as M | M+ || X- | X, the standard reduction potentials are E°(M+/M) = 0.44 V and E°(X/X-) = 0.33 V. Which conclusion is valid from this information?

1. The spontaneous overall reaction is M + X → M+ + X-
2. The spontaneous overall reaction is M+ + X- → M + X
3. The standard cell potential is 0.77 V
4. The standard cell potential is -0.77 V

Correct answer: The spontaneous overall reaction is M+ + X- → M + X

Solution

As written, M is the anode and X the cathode: Ecell = E(X/X-) - E(M+/M) = 0.33 - 0.44 = -0.11 V. Since Ecell < 0, the forward reaction is non-spontaneous and the spontaneous reaction is the reverse: M+ + X- -> M + X.

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