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    I'm really struggling with this question:

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    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.

    Please could someone explain why.

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

    Name:  2016-06-17.png
Views: 32
Size:  114.1 KB

    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.

    Please could someone explain why.

    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
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    (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! :woo:
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    (Original post by alde123)
    Thank you so, so much! You are literally a genius! :woo:
    lol wouldn't say that, but I am glad to help
 
 
 
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