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Determining rate of reaction with respect to reactants watch

1. http://qualifications.pearson.com/co...e_20130114.pdf

Q18, I understand why it's second order with respect to H+, but don't understand the rate with respect to Br-.

I thought you have to factor in the BrO3- (and the fact that is first order)
2. (Original post by indignation)
http://qualifications.pearson.com/co...e_20130114.pdf

Q18, I understand why it's second order with respect to H+, but don't understand the rate with respect to Br-.

I thought you have to factor in the BrO3- (and the fact that is first order)
Between expts 1 & 2 you can see the effect of doubling the H+ concentration.

Well in experiment 3 you have halved the H+ concentration so you would expect the rate to be the same as expt 1 APART from the effect of the bromide ion change and the bromate ion change.

However, you are told that the bromate order is 1, so you can already factor that into the expected answer:

Expt 1 rate = 1.68 x 10-5

now factor in the bromate change (it has increased by a factor of 3, so the rate should also)

5.04 x 10-5

But the actual rate is 1.10 x -5, i.e. double

The reason for the double is the change in bromide concentration, which has also doubled.

Hence the order wrt bromide = 1

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