CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
A single starting material, R, can undergo two competing one-step transformations to produce either kinetic product K or thermodynamic product T. Energetic measurements at 298 K give the following standard free energies (all values in kJ mol⁻¹ relative to R):
• Transition state leading to K: +60
• Product K: +5
• Transition state leading to T: +120
• Product T: –40
(a) Construct a reaction coordinate diagram that includes both pathways on the same set of axes. Label each transition state and product, and indicate all relevant energy differences numerically.
(b) Identify which product will predominate in the reaction mixture immediately after the reaction is quenched at 298 K. Provide a quantitative or semiquantitative justification that references the data above.
(c) After the mixture from part (b) is maintained at 298 K for an extended period, its composition changes. Predict the final predominant product and explain the driving force for this change.
(d) The reaction is now repeated at 425 K. Predict how the product distribution obtained upon rapid quench at this higher temperature will differ from that at 298 K, and justify your answer in terms of the temperature dependence of the relevant kinetic parameters.