Direction: The standard redox potential values for two half-reactions are given below. The value for Faraday’s constant is 96.48 kJ V–1 mol–1 and Gas constant R is 8.31 JK–1 mol–1.
NAD+ + H+ + 2e- ? NADH – 0.315 V
FAD + 2H+ + 2e– ? FADH2 – 0.219 V
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The value of ?G', given Keq as 1.7, at 23°C will be
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- – 17.19 kJ mol–1
- – 19.8 kJ mol–1
- + 52.82 kJ mol–1
- – 117.07 kJ mol–1
Correct Option: A
We know, ΔG’ = ΔG° + RT log Keq
Where, ΔG’= change in Gibbs free energy
ΔG° = standard change in Gibbs free energy
R = Universal Gas constant
T = absolute temperature
Keq = equilibrium constant
Given,
ΔG° = –18.5 kJ/mol, R= 8.31 J/K/mol
= 8.31 * 10–3 kJ/K/mol, Keq = 1.7,
T = 230C = (273 + 23) K = 296K
Therefore,
ΔG’= –18.5 + [8.31 * 10–3 *296 * log(1.7)]
= –17.19 kJ/mol
Therefore the value of ΔG’ is –17.19 kJ/mol
