Q.41 The actual free energy change of a given biochemical reaction carried out under standard
conditions with 1 M initial concentration of each of the reactants and products will be
(A) equal to zero
(B) equal to standard free energy change for the reaction
(C) less than the standard free energy change for the reaction
(D) greater than the standard free energy change for the reaction
Free Energy Change in Biochemical Reactions: Standard vs Actual ΔG Explained
The actual free energy change (ΔG) for a biochemical reaction under standard conditions with 1 M initial concentrations equals the standard free energy change (ΔG°).
Correct Answer
Answer: (B) equal to standard free energy change for the reaction
Standard conditions define ΔG° precisely as the free energy change when all reactants and products start at 1 M concentration, 25°C, pH 7, and 1 atm pressure. This matches the query’s setup exactly, so ΔG = ΔG°.
ΔG vs ΔG° Key Difference
Standard free energy change (ΔG°) is constant for a reaction, based on equilibrium constant K under defined conditions.
Actual free energy change (ΔG) follows ΔG = ΔG° + RT ln Q, where Q is the reaction quotient from current concentrations.
When initial [reactants] =
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Option Analysis
-
(A) equal to zero: Incorrect. ΔG = 0 only at equilibrium, not under initial standard conditions unless K = 1 (ΔG° = 0).
-
(B) equal to standard free energy change: Correct, as explained above.
-
(C) less than the standard free energy change: Wrong. ΔG equals ΔG° here; it could be less negative if Q > 1 in non-standard cases.
-
(D) greater than the standard free energy change: Incorrect. No deviation occurs at Q = 1; ΔG becomes more positive only if Q > 1.
| Option | Why Incorrect/Correct | Key Equation Insight |
|---|---|---|
| (A) Zero | Equilibrium only | ΔG = 0 when Q = K |
| (B) Equal to ΔG° | Matches definition | Q = 1 → ΔG = ΔG° |
| (C) Less than ΔG° | No basis at 1 M | Requires Q < 1 |
| (D) Greater than ΔG° | No basis at 1 M | Requires Q > 1 |
Keywords: free energy change, biochemical reaction, standard conditions, ΔG vs ΔG°, 1 M concentration, Gibbs free energy, biochemistry MCQ
