At equilibrium, the reaction A ⇌ B + C has the following reactant concentrations: [A] = 3 mM, [B] = 4 mM, and [C] = 10 mM. What is the standard free energy change for the reaction & is it endergonic or exergonic?

• A. – 6418 J
• B. 6418 J
• C. 10,698 J
• D. – 10,698 J

Answer: (C)

Verified step by step guidance

1. Identify the reaction and the concentrations of the reactants and products at equilibrium: A ⇌ B + C, with [A] = 3 mM, [B] = 4 mM, and [C] = 10 mM.
2. Use the equilibrium constant expression for the reaction: K_eq = ([B][C]) / [A]. Substitute the given concentrations into this expression to calculate K_eq.
3. Recall the relationship between the standard free energy change (ΔG°) and the equilibrium constant (K_eq): ΔG° = -RT ln(K_eq), where R is the universal gas constant (8.314 J/mol·K) and T is the temperature in Kelvin.
4. Assume the temperature is 298 K (standard conditions) unless otherwise specified. Substitute the values of R, T, and the calculated K_eq into the equation to find ΔG°.
5. Determine if the reaction is endergonic or exergonic based on the sign of ΔG°. If ΔG° is negative, the reaction is exergonic; if positive, it is endergonic.