You are Here: Home

# Rate constants

Announcements Posted on
TSR's new app is coming! Sign up here to try it first >> 17-10-2016
1. I'm really struggling with this question:

So far I've written (the bit that's wrong is in italics):

Comparing experiments 1 and 2:
[O3(g)] quadruples and [C2H4(g)] stays the same.
The rate also quaruples so reaction is 1st order with respect to [O3(g)].

Experiments 3 and 2:
[O3(g)] and [C2H4(g)] doubles, the rate quadruples so the reaction is 2nd order with respect to [C2H4(g)].

The mark scheme says this is wrong and that the reaction is 1st order.

Thanks
2. (Original post by alde123)
I'm really struggling with this question:

So far I've written (the bit that's wrong is in italics):

Comparing experiments 1 and 2:
[O3(g)] quadruples and [C2H4(g)] stays the same.
The rate also quaruples so reaction is 1st order with respect to [O3(g)].

Experiments 3 and 2:
[O3(g)] and [C2H4(g)] doubles, the rate quadruples so the reaction is 2nd order with respect to [C2H4(g)].

The mark scheme says this is wrong and that the reaction is 1st order.

Thanks
Yep, so the marking scheme is correct. Your reasoning for the constant w.r.t ozone is also correct. Now, for the constant w.r.t ethene, your choice of experiment is correct. However, now comes the tricky bit. The conc. of ozone doubled, so the effect ozone would have on the rate would be that it would double as well, correct? So if you considered ozone alone, the new rate ought to have risen from 4 to 8. BUT it rose to 16, DOUBLE of 8, meaning that ethene had an effect on the rate. We doubled ethene's conc. as well, and this doubled the rate of reaction from 8 to 16, hence it is first order wrt to ethene as well.Hope this helped
3. (Original post by ssshah2)
Yep, so the marking scheme is correct. Your reasoning for the constant w.r.t ozone is also correct. Now, for the constant w.r.t ethene, your choice of experiment is correct. However, now comes the tricky bit. The conc. of ozone doubled, so the effect ozone would have on the rate would be that it would double as well, correct? So if you considered ozone alone, the new rate ought to have risen from 4 to 8. BUT it rose to 16, DOUBLE of 8, meaning that ethene had an effect on the rate. We doubled ethene's conc. as well, and this doubled the rate of reaction from 8 to 16, hence it is first order wrt to ethene as well.Hope this helped
Thank you so, so much! You are literally a genius!
4. (Original post by alde123)
Thank you so, so much! You are literally a genius!
lol wouldn't say that, but I am glad to help

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: June 17, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### How does exam reform affect you?

From GCSE to A level, it's all changing

### Who would you like to thank?

Poll
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.