![]() ![]() ![]() Remember that even though there are different numbers of electrons in each half-reaction, the cell potential for the cathode is not multiplied by two when determining the standard cell potential. The reaction involves an oxidation-reduction reaction, so the standard cell potential can be calculated using the E° reduction data in Appendix K.Īnode (oxidation): Fe(s) → Fe 2 (aq) 2 e – E° Fe 2 /Fe = -0.44 VĬathode (reduction): Ag (aq) e – → Ag(s) E° Ag /Ag = 0.80 VĮ° cell = E° cathode – E° anode = E° Ag /Ag – E° Fe 2 /Fe = 1.24 V What is the standard free energy change and equilibrium constant for the following reaction at 25 ☌? Given any one of the three quantities, the other two can be calculated, so any of the quantities could be used to determine whether a process was spontaneous.Įquilibrium Constants, Standard Cell Potentials, and Standard Free Energy Changes The relationships between ΔG°, K, and E°cell. The relationships are shown graphically in Figure 1. Thus, if Δ G°, K, or E° cell is known or can be calculated, the other two quantities can be readily determined. For historical reasons, the logarithm in equations involving cell potentials is often expressed using base 10 logarithms (log), which changes the constant by a factor of 2.303: Where n is the number of moles of electrons. Collecting terms at this temperature yields: Most of the time, the electrochemical reactions are run at standard temperature (298.15 K). This provides a way to relate standard cell potentials to equilibrium constants, since: Thus, spontaneous reactions, which have Δ G 0. We can verify the signs are correct when we realize that n and F are positive constants and that galvanic cells, which have positive cell potentials, involve spontaneous reactions. If all the reactants and products are in their standard states, this becomes: This equation can be related to free energy with the following equation ![]() Hence, the total quantity of charge transferred is, where n is the number of moles of electrons for the balanced oxidation-reduction reaction: ![]() The electrical work is the product of the charge transferred multiplied by the potential difference (voltage):Įlectrical work (J) = volts × charge in coulombs In galvanic cells, chemical energy is converted into electrical energy, which can do work. We will now extend electrochemistry by determining the relationship between E° cell and the thermodynamics quantities such as Δ G° (Gibbs free energy) and K (the equilibrium constant). | Key Concepts and Summary | Key Equations | Glossary | End of Section Exercises | ΔG°, K°, and E° cell Interpret results from Nernst equation calculations to determine whether a reaction will form more reactants or products in order to achieve equilibrium.Apply the Nernst equation to calculate the potential for a cell under non-standard state conditions or to calculate an unknown concentration in an electrochemical cell.Calculate E° from ΔG° or K for a redox reaction.Sn 2 (aq) 2e - → Sn (s) with SRP E o = -0.137 V (Cathode where reduction happens)Ģ. \) for the voltaic cell formed by each reaction.ġ.a) Ba 2 (aq) → Ba (s) 2e- with SRP (for opposite reaction) E o = -2.92 V (Anode where oxidation happens)Ĭu 2 (aq) 2e- → Cu (s) with SRP E o = 0.340 V (Cathode where reduction happens)ġ.b) Al 3 (aq) → Al (s) 3e - with SRP (for opposite reaction) E o = -1.66 V (Anode where oxidation happens) ![]()
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