Chemistry
Chemistry
Problem
Reactants are defined at 0 kJ·mol⁻¹. The uncatalyzed mechanism for a reaction proceeds through three transition states with energies of 50 kJ·mol⁻¹, 90 kJ·mol⁻¹, and 80 kJ·mol⁻¹, respectively. A catalyst lowers the energy of the second transition state by 55 kJ·mol⁻¹, leaving the other two unchanged. Identify the rate-determining transition state for the catalyzed pathway and state the overall activation energy, in kJ·mol⁻¹, for the catalyzed reaction, using the given values to justify your answer.Intuitive explanation
The rate-determining step is the one with the highest activation energy—the slowest bottleneck that controls overall reaction speed. When a catalyst lowers one transition state's energy, you need to recalculate all three barriers from reactants and identify which is now tallest. The overall activation energy is determined by whichever transition state remains highest; the catalyst helps by reducing one barrier, but if another barrier is still higher, that becomes the new rate-limiting step.
Intuitive explanation
The rate-determining step is the one with the highest activation energy—the slowest bottleneck that controls overall reaction speed. When a catalyst lowers one transition state's energy, you need to recalculate all three barriers from reactants and identify which is now tallest. The overall activation energy is determined by whichever transition state remains highest; the catalyst helps by reducing one barrier, but if another barrier is still higher, that becomes the new rate-limiting step.