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Chemistry rates calculation help

http://qualifications.pearson.com/content/dam/pdf/A%20Level/Chemistry/2013/Exam%20materials/6CH04_01_que_20130114.pdf

January 2013 edexcel unit 4

Question 8 help please.

I got the order wrt [H+] =2nd order

I'm stuck with [Br-]
looking at experiment 1 and 3, [Br-] doubles, [BrO3-] triples and [H+] stays constant. The rate increases by x6 but does this all link to get 1st order wrt [Br-]

Thanks x

bump

Original post by Dinaa

@Kvothe the arcane??

Reply 3

Dinaa

Original post by thefatone

@Kvothe the arcane??

thanks

Reply 4

VanEkerDr

The rate is 1st order with respect to bromide. You can work this out by what they tell you in the question. You've already correctly determined that the rate is 2nd order with respect to H+. Knowing that the order is 1st order with respect to bromate, you now have enough information to work out the order with respect to bromide.

As you've stated, the rate increases 6-fold when you increase the concentration of bromate by a factor of 3 and the concentration by a factor of 2. Knowing that the rate with respect to bromate is 1st order, the rate should triple with a 3-fold increase in the concentration of bromate. Now if the rate was 2nd order with respect to bromide then if you doubled the concentration the rate should increase 4-fold. If it was zero order the concentration of bromide would not affect the rate. As the rate doubles with a 2-fold increase in the concentration of bromide.. you can infer that the rate is 1st order with respect to bromide.