Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: vamosvaxn on February 23, 2015, 03:10:33 PM
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In my OCR A-Level Chemistry there is a practice question I have completed but I am unsure how the answer the book gives is calculated.
The question is this:
The reaction between ozone, O3(g), and ethane, C2H4(g) has the following rate equation -
Rate = k[O3(g)] [C2H4(g)]
(Note that it states both ozone and ethane are first orders (power of 1))
5.0 x 10^-8 mol dm^-3 O3(g) was reacted with 1.0 x 10^-8 mol dm^-3 C2H4(g). The initial rate of reaction was 1.0 x 10^-12 mol dm^-3 s^-1.
Calculate the rate constant, k, for this reaction and state its units.
When I calculated this, my answer was k = 2 x 10^13 dm^3 mol^-1 s^-1
But when I checked the answer in the book it said the correct answer is k = 8.3 x 10^4 dm^6 mol^-2 s^-1
If I’m not mistaken, this would imply that either ozone or ethane is a second order (power of 2/squared). But it clearly states in the rate equation that both reactants are first orders. Is this a printing error, or is there something I am missing?
Thanks!
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The book's answer is obviously wrong (did you look up the wrong answer by mistake? or did they print the answer to the wrong question?). If one of the reagents was second order, you would have a product of the order of 10-24, and a k of the order of 1012. And how would you get the factor 8.3 from a simple combination of the factors 5, 1 and 1?
Your own answer is also wrong - the answer is 2 x 103 (not 1013) L/mol/s.
And C2H4 is ethene. (That might not be a mistake. I've just noticed it autocorrects ethene to ethane. Is it possible to turn autocorrect off?)