9.4 Thermodynamic and Kinetic Control

Explain, in terms of kinetics, why a thermodynamically favored reaction might not occur at a measurable rate.

• Many processes that are thermodynamically favored do not occur to any measurable extent, or they occur at extremely slow rates.
• Processes that are thermodynamically favored, but do not proceed at a measurable rate, are under “kinetic control.” High activation energy is a common reason for a process to be under kinetic control. The fact that a process does not proceed at a noticeable rate does not mean that the chemical system is at equilibrium. If a process is known to be thermodynamically favored, and yet does not occur at a measurable rate, it is reasonable to conclude that the process is under kinetic control.