## 15.51

$K = \frac{k_{forward}}{k_{reverse}}$

Pooja Nair 1C
Posts: 55
Joined: Thu Jul 13, 2017 3:00 am

### 15.51

How do you determine which of the steps is the rate-controlling step? Is it just the slower one/Why?

soniatripathy
Posts: 50
Joined: Thu Jul 13, 2017 3:00 am

### Re: 15.51

yes, you are right! the rate determining step will be the slow one. This is because the slow step is the one that takes more time, but once that step is complete the fast steps can immediately complete the mechanism. Imagine a relay race, if there is a slow runner, that person is likely to play a major role in determining the rate of the race because they take the most time. once that runner has completed their section, the faster runners can quickly finish the race without having much effect on the rate.
the book also gives the following example: "A rate-determining step is like a slow ferry on the route between two cities. The rate at which the traffic arrives at its destination is governed by the rate at which it is ferried across the river, because that part of the journey is much slower than any of the others. Steps that follow the rate-determining step take place as soon as the intermediate has been formed and have a negligible effect on the overall rate. There- fore, they can be ignored when writing the overall rate law from the mechanism."