## rate law from elementary step

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

Maeve Gallagher 1J
Posts: 56
Joined: Fri Sep 29, 2017 7:07 am

### rate law from elementary step

Why can you use the equation for the slowest elementary step, i.e. the stoichiometric coefficients for order, when writing out that steps rate law?

Yashaswi Dis 1K
Posts: 56
Joined: Fri Sep 29, 2017 7:04 am

### Re: rate law from elementary step

I don't think you can use the stoichiometric coefficients from the slow determining step but you can use the reactants and see if what type of molecular reaction it is (i.e. bimolevular, trimolecular, etc.). We use it from the slow-rate determining step because that is the reaction that if it's slow then, the rate will be "determined" by that step, so that's why we look at the slow-step.

Juanyi Tan 2K
Posts: 33
Joined: Fri Sep 29, 2017 7:05 am

### Re: rate law from elementary step

Because the slow step kinetically controls the rate of a chemical reaction, the rate law can be determined by looking at the reactants involve in the slow step. That is why we can use the stoichiometric coefficient from slow step to write out the rate law for the whole reaction.