During an investigation of an ester hydrolysis in aqueous solution
CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
During an investigation of an ester hydrolysis in aqueous solution, students use a computer program to calculate the system’s Gibbs free energy as a function of the extent of reaction, ξ (in mol) at 298 K. The program outputs the following qualitative features of the ΔG versus ξ curve:
• At ξ = 0, ΔG = +4.5 kJ.
• ΔG decreases steeply at first, then flattens, crossing zero at ξ = 0.36 mol.
• The curve reaches a minimum value of –0.72 kJ at ξ = 0.42 mol.
• Beyond ξ = 0.42 mol, ΔG rises gradually, returning to ΔG = 0 at ξ = 0.49 mol.
Answer the questions below concerning the thermodynamic information contained in this curve.
(a) Sketch a qualitative graph of ΔG versus ξ that is consistent with the description. Label all key points mentioned.
(b) Identify the value(s) of ξ corresponding to equilibrium for the uncatalyzed reaction. Explain your reasoning.
(c) Explain how the slope of the ΔG versus ξ curve at any point relates to the direction and magnitude of the reaction’s driving force at that composition.
(d) Propose, with justification, how the addition of a catalyst would modify the shape or position of the ΔG versus ξ curve, if at all, and discuss the implication for the equilibrium position.