## 7A.15

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

Posts: 134
Joined: Sat Sep 14, 2019 12:17 am

### 7A.15

Why is it that when writing the rate law for the reaction (=k[A][B]^2) that the b is squared and the a isn't?
Last edited by Ghadir Seder 1G on Tue Mar 10, 2020 2:32 pm, edited 1 time in total.

alicechien_4F
Posts: 104
Joined: Sat Jul 20, 2019 12:15 am

### Re: 7b.15

Did you by chance post the wrong question? I can't seem to find the corresponding question for 7B15. But in general, the B is squared because it is a second order reaction, while the A is not because it is first order.

Naneeta Desar 1K
Posts: 106
Joined: Fri Aug 09, 2019 12:15 am

### Re: 7b.15

Generally when a reactant in the rate equation is squared it is 2nd order.

jisulee1C
Posts: 149
Joined: Thu Jul 25, 2019 12:17 am

### Re: 7b.15

it depends on whether the reaction is the elementary rate law. If the reaction is the elementary reaction one can assume that the exponent is the order in relation to the reactant. Therefore if b is squared the it is in second order while if a is to the power of 1 it is in first order. If you cannot assume that the reaction is elementary you have to find the unique rate using stoichiometric coefficients.

Posts: 134
Joined: Sat Sep 14, 2019 12:17 am

### Re: 7A.15

apologies, I meant 7A.15, not 7B.15 :)

Posts: 134
Joined: Sat Sep 14, 2019 12:17 am

### Re: 7A.15

How do we decide which experiments to use to determine the rates with respect to A and B?

thank you!

Ryan Chang 1C
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Joined: Sat Aug 24, 2019 12:17 am

### Re: 7A.15

Ghadir Seder 1G wrote:How do we decide which experiments to use to determine the rates with respect to A and B?

thank you!

First, you have to realize that C is zero order reactant. Now that C is independent and doesn't affect the other concentrations, to find the order of A, compare experiments 2 and 4 because the concentration of A changes while the concentration of B remains constant. To find the order of B, compare experiments 2 and 3 because the concentration of B changes while the concentration of A remains constant.