CHEMISTRY · Single correct · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
A reactant R can form two products, P and Q.
• Activation energy to P: 35 kJ mol⁻¹
• Activation energy to Q: 60 kJ mol⁻¹
• ΔG°(P): +8 kJ mol⁻¹
• ΔG°(Q): –15 kJ mol⁻¹
The reaction is run at –78 °C for 30 s and then rapidly quenched. Which product is most likely to be isolated in greatest amount?
(a) Q, because it is thermodynamically more stable (more negative ΔG∘).
(b) Q, because the larger driving force (ΔG∘) more than compensates for the higher activation energy even at −78∘C.},{
(c) P, because the pathway to P has the lower activation energy (kinetic control).
(d) Approximately equal amounts of P and Q, because the temperature is too low for either pathway to dominate.