JEE Advanced levelOne or more correct optionsDifficulty 3 of 3g3216
A mixture of products K and T forms from a reactant and is under thermodynamic control. Which statements are correct?
AOnce equilibrium is reached, the ratio [T]/[K] no longer changes with time
BThe ratio of products is fixed by the relative energies of the transition states leading to K and T
CThe product with the lowest activation energy always predominates
DIf T is more stable than K by ΔG∘=5.7kJmol−1 at 298 K, then [T]/[K] ≈ 10
Answer: A, D
Thermodynamic control means the products equilibrate, so the ratio is time-independent and equals Keq=exp(5700/(8.314×298))=9.98. Transition-state energies and the lowest activation energy determine the ratio only under kinetic control.