## Limiting Step

$\frac{d[R]}{dt}=-k[R]^{2}; \frac{1}{[R]}=kt + \frac{1}{[R]_{0}}; t_{\frac{1}{2}}=\frac{1}{k[R]_{0}}$

Sylvester_Foley_3G
Posts: 11
Joined: Wed Sep 21, 2016 2:59 pm

### Limiting Step

When we are given problems that involve the fast step and the slow step, how can we tell which step is the limiting step?

Sylvester :)

david_li3H
Posts: 16
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Limiting Step

The slow step is always the limiting step.

John Huang 1G
Posts: 46
Joined: Thu Jul 13, 2017 3:00 am
Been upvoted: 1 time

### Re: Limiting Step

Apparently, the step with the higher activation energy is often times the limiting step as well. High activation energies are associated with slower rates due to the large amount of energy needed for the step to be thermodynamically favorable.

Maria Bajenov 1I
Posts: 28
Joined: Fri Sep 29, 2017 7:06 am

### Re: Limiting Step

Since we haven't covered activation energy, do we always determine the slow step with the determined rate law? Is there any other method we have learned to determine the slow step?

Guangyu Li 2J
Posts: 50
Joined: Fri Sep 29, 2017 7:07 am
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### Re: Limiting Step

The slow step is associated with higher activation energy because it needs to overcome the higher energy barrier, while the fast step is associated with lower activation energy because it needs to overcome the lower energy barrier. As a result, the slow step always the limiting step because it always takes the most amount of energy in the overall reactions.

Ashley Garcia 2L
Posts: 33
Joined: Fri Sep 29, 2017 7:05 am

### Re: Limiting Step

The reaction rate is always dependent on the slow step, which is the limiting step. The slow step has the highest activation energy out of all the steps, and therefore has the slowest reaction rate because more energy is needed to overcome the activation energy barrier.

Akash_Kapoor_1L
Posts: 52
Joined: Thu Jul 13, 2017 3:00 am
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### Re: Limiting Step

Do we have to know how to calculate the limiting step for test 3? Which hw problems focus on the limiting step?

joycelee1A
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

### Re: Limiting Step

Akash_Kapoor_1L wrote:Do we have to know how to calculate the limiting step for test 3? Which hw problems focus on the limiting step?

I don't think so. Dr. Lavelle said test three would go up to 15.6, and this topic isn't on there.