## How to use general rate laws to find rates of specific equations?

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

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ashwathinair
Posts: 113
Joined: Sat Aug 17, 2019 12:17 am

### How to use general rate laws to find rates of specific equations?

How do you use rate laws to find the rate of a specific reaction? For example, in 7C 1:
Each of the following is an elementary reaction. Write its rate law and state its molecularity. (a) NO + NO --> N2O2; (b) Cl2 --> Cl + Cl.

JamieVu_2C
Posts: 108
Joined: Thu Jul 25, 2019 12:16 am

### Re: How to use general rate laws to find rates of specific equations?

Since these are elementary reactions, you can write the rate law using the coefficients. For part a, since there are 2 NO molecules on the reactant side, the rate = k[NO]^2, and it is bimolecular. For part b, there is only 1 Cl2 molecule, so the rate = k[Cl2], and it is unimolecular.

Daria MacAuslan 1H
Posts: 50
Joined: Sat Aug 17, 2019 12:16 am

### Re: How to use general rate laws to find rates of specific equations?

Rate laws can be used in this question because for bimolecular reactions like the one in part a, the rate is simply equal to k[NO}^2, because there are two molecules of NO reacting and colliding with each other. This makes the coefficient for NO 2, and thus that becomes the exponent in the rate law (since this is an elementary reaction). In the second one, the rate can be just written as rate=k[Cl2] since it is unimolecular.

ashwathinair
Posts: 113
Joined: Sat Aug 17, 2019 12:17 am

### Re: How to use general rate laws to find rates of specific equations?

Daria MacAuslan 1H wrote:Rate laws can be used in this question because for bimolecular reactions like the one in part a, the rate is simply equal to k[NO}^2, because there are two molecules of NO reacting and colliding with each other. This makes the coefficient for NO 2, and thus that becomes the exponent in the rate law (since this is an elementary reaction). In the second one, the rate can be just written as rate=k[Cl2] since it is unimolecular.

Wait, but I thought order is independent of stoichiometric coefficients?

ashwathinair
Posts: 113
Joined: Sat Aug 17, 2019 12:17 am

### Re: How to use general rate laws to find rates of specific equations?

Wait never mind, I found the unimolecular/bimolecular info in my notes! Thanks!

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