## slow step

$aR \to bP, Rate = -\frac{1}{a} \frac{d[R]}{dt} = \frac{1}{b}\frac{d[P]}{dt}$

chloewinnett1L
Posts: 55
Joined: Fri Sep 28, 2018 12:20 am

### slow step

How do we determine which step in a multistep reaction is the slow step? Or will that always be given?

Jim Brown 14B Lec1
Posts: 62
Joined: Fri Sep 28, 2018 12:28 am

### Re: slow step

It is either stated explicitly or has the smaller k value

Searra Harding 4I
Posts: 68
Joined: Fri Sep 28, 2018 12:29 am

### Re: slow step

Jim Brown 14B Lec1 wrote:It is either stated explicitly or has the smaller k value
Why does the slow step have a smaller k value conceptually speaking?

Jack DeLeon 1B
Posts: 30
Joined: Fri Sep 28, 2018 12:20 am

### Re: slow step

the k value is the rate constant in the rate equation, so if the rate constant is small, then the rate is slow

Jennifer Lathrop 1F
Posts: 71
Joined: Sat Dec 02, 2017 3:00 am

### Re: slow step

is there a conceptual way to know if an equation is the slow step just by looking at it? Such as if some molecules are known to react together slower?

allisoncarr1i
Posts: 60
Joined: Fri Sep 28, 2018 12:15 am

### Re: slow step

Jack DeLeon 1B wrote:the k value is the rate constant in the rate equation, so if the rate constant is small, then the rate is slow

do you know why this is the case?

Brian Chang 2H
Posts: 65
Joined: Fri Sep 28, 2018 12:17 am

### Re: slow step

The slow step will either be explicitly referred to as the "Slow step" or it will be implicit by having a lower k value than the other steps. Indicating that it is the slowest step.

Kyither Min 2K
Posts: 60
Joined: Wed Oct 03, 2018 12:15 am

### Re: slow step

It will typically be told as the slow step or if it's in a proposed mechanism, I think we are expected to deduce which is the slow step based on the experimentally determined rate law.

Destiny Diaz 4D
Posts: 51
Joined: Fri Sep 28, 2018 12:28 am

### Re: slow step

why is it important to know which step is the slower or the faster one? is it just to ensure that the k values are correct and accurate ?

Claudia Luong 4K
Posts: 59
Joined: Fri Sep 28, 2018 12:25 am

### Re: slow step

In most of the problems we've done, it seems to be explicitly stated in the problem.

Isabelle Fontanilla 1I
Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

### Re: slow step

You can also look at the rate values(if given) and compare--the bigger the rate, the faster it is. The rate constant, k, is directly proportional to the rate, so the bigger the k, the bigger the rate=faster reaction. The rate determining step, being the slowest, should usually have the smallest k and, therefore, rate.

Rami_Z_AbuQubo_2K
Posts: 89
Joined: Thu Jun 07, 2018 3:00 am

### Re: slow step

If you know that the reaction is a pre-equilibrium reaction, then the second step will be the slow one. That first step is going to be a fast reaction and it is considered to be at equilibrium where there is a bottle necking effect and that leads into your second step which is going to be the rate determining step. If the problem is not at equilibrium, then you they must give you the reaction rate or they must tell you which is slow and which is fast.