A chemist is evaluating three independent redox reactions under standard conditions at 298 K. The measured standard free-energy changes are listed in the table.
Reaction I ΔG° = −45 kJ mol⁻¹
Reaction II ΔG° = +12 kJ mol⁻¹
Reaction III ΔG° = −2.3 kJ mol⁻¹
a. Rank the equilibrium constants for the three reactions from largest to smallest. Provide a clear justification that connects the numerical values of ΔG° to the relative magnitudes of K without using precise calculations.
b. Identify which reaction will have the equilibrium mixture containing at least 99 % products. Support your choice with quantitative reasoning that includes an appropriate threshold for K.
c. For Reaction II, the chemist proposes coupling it with Reaction I so that the overall process becomes thermodynamically favorable. Predict the sign of ΔG° for the coupled process and describe, in terms of the individual K values, how the overall equilibrium constant compares with 1.