## 15.19 [ENDORSED]

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

sofiakavanaugh
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Joined: Thu Jul 13, 2017 3:00 am
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### 15.19

For this problem, there is a big table full of experimental values and you are asked for the rate law. I was confused on how to calculate the order of B, sorry I cant type the table but if someone could explain to me how they did it that would be amazing.

Thanks

Sammy Thatipelli 1B
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Joined: Thu Jul 27, 2017 3:01 am
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### Re: 15.19

to calculate the order of b, use experiments 2 and 3. increasing the concentration of B by the ratio 3.02/1.25 increases the rates by (3.02/1.25)^2, and this makes B second order.

Andrew Nguyen 2I
Posts: 68
Joined: Fri Sep 29, 2017 7:07 am

### Re: 15.19  [ENDORSED]

Sometimes the order number can be seen by simple observation, though it's better to have a foolproof method for rates like this. The rate changes by a ratio of 50.8/8.7 and the concentration by 3.02/1.25

So, simply equate the concentration raised by the order number equal to rate

(3.02/1.25)^x = 50.8/8.7

where x is the order number; you get 2.416^x = 5.84

take the log of both sides, allowing you to take x down by the log power rule:
x*log2.416 = log 5.84

simplify

x = log2.416/log5.84

You get something very close to 2 such as 1.99, giving you a second order power.