Question

Electrochemical Cell Potentials

Table 1: Electrochemical Cell Potentials
Cell	Measured Total Potential from Multimeter (V)1	Individual Half-Cell Potentials				Cell Reactions5	ΔG (kJ)6
		(Cu) Electrode Standard Potential (V)2	Metal Electrode Experimental Potential (V)3	Metal Electrode Theoretical Potential (V)4	Metal Electrode Potential % Error
Cu | Sn	0.469	0.34 V	0.34-0.469 =-0.129			Cathode:       Cu2+ + 2e- -> Cu
						Anode:            Sn ->Sn2++ 2e-
						Net:          Cu2+ + Sn -> Cu + Sn2+
Cu | Al	0.796	0.34 V	0.34-0.796 =-0.456			Cathode:   Cu2+ + 2e- -> Cu
						Anode:   Al ->Al3++ 3e-
						Net: 3Cu2+ + 2Al-> 3Cu + 2Al3+
Cu | Fe	0.579	0.34 V	0.34-0.579 =-0.239			Cathode:        Cu2+ + 2e- -> Cu
						Anode:            Fe ->Fe2++ 2e-
						Net:                  Cu2+ + Fe -> Cu + Fe2+
Cu | Zn	1.02	0.34 V	0.34-1.02 =-0.68			Cathode:     Cu2+ + 2e- -> Cu
						Anode:        Zn ->Zn2++ 2e-
						Net:              Cu2+ + Zn -> Cu + Zn2+

The voltage of an electrochemical cell is also related to the Gibbs free energy of its chemical reaction through the relationship of ΔG = -nFE, where n is the number of electrons transferred in the balanced equation, E is the cell's voltage, and F is the Faraday constant (96,485 C/mol).

(a) In order for a reaction to occur (be spontaneous), what must be the sign (+/-) for ΔG?

(b) Under spontaneous circumstances, then, what must be the sign (+/-) for E (your voltage)?

(c) Knowing the answers to (a) and (b) above, how can one deduce the direction of spontaneity for a particular voltaic cell reaction by using only a voltmeter without doing any calculations

(a) Rank your electrochemical cells in this experiment in order of decreasing voltage (V) and decreasing Gibbs free energy (ΔG). Is the ranking the same in both cases? If not, explain what that may be the case.

(b) How is knowing ΔG in addition to V helpful when considering an electrochemical cell?

Answer 1