## Determining Intermediates/Catalysts - #14.47

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

Megan White 2C
Posts: 18
Joined: Fri Sep 26, 2014 2:02 pm

### Determining Intermediates/Catalysts - #14.47

Hello All!

In Lecture on Friday, Dr. Lavelle introduced the topic of catalysts, and within his explanation, he mentioned that catalysts are involved in chemical RXNs, but they are neither reactants nor products, nor are they PRODUCED in the chemical RXN at hand.

With all of that in mind, in working through homework problem #14.47, why is it that (NO) is the catalyst within the overall RXN? In Step 2, NO is PRODUCED from the combination of NO2 + O. Wouldn't this discount NO as a catalyst, rendering it another intermediate molecule instead?

Thanks so much for any and all help!

Kayla Denton 1A
Posts: 106
Joined: Fri Sep 26, 2014 2:02 pm

### Re: Determining Intermediates/Catalysts - #14.47

A quick way to tell the difference between a catalyst and an intermediate is to see whether it is present at the beginning of the reaction.

Intermediates are first produced and then consumed in the reaction, so they're not present as reactants in the beginning.
Catalysts, on the other hand, are always present as reactants at the beginning. (They are also present as products at the end.)

I wouldn't worry about individual reactions but just look at the 'big picture' to distinguish between catalysts and intermediates.
Hope that helped :)

Megan White 2C
Posts: 18
Joined: Fri Sep 26, 2014 2:02 pm

### Re: Determining Intermediates/Catalysts - #14.47

Thanks Kayla!

Justin Le 2I
Posts: 142
Joined: Fri Sep 26, 2014 2:02 pm

### Re: Determining Intermediates/Catalysts - #14.47

Catalysts are consumed and then produced so there is no net change. Intermediates are produced and then consumed. So in chemical equations, you will see catalysts first appear on the reactants side and you will see intermediates first appear on the products side.

martha-1I
Posts: 76
Joined: Fri Sep 26, 2014 2:02 pm

### Re: Determining Intermediates/Catalysts - #14.47

NO is a catalyst because it is consumed (in step 1) and then formed (in step 2).

A nice way to think of what is happening is to envision what is happening when a catalyst is introduced into a reaction. Key word being introduce, which implies that the catalyst is not formed first but just appears. Catalyst are introduced into an reaction to speed it up, but in the process they get consumed by the reaction and then are formed again in a later step.