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# Chemistry A-Level rates question! watch

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1. The question:

The activation energy for the forward reaction is 184 kJ mol−1.
2HI(g) U H2(g) + I2(g)

At 700 K, the rate constant is 2.32 × 10−3 dm3
mol−1 s−1.

Calculate the rate constant at 800 K and give your answer to three significant figures.
You should not attempt to use any graphical method to answer this question.
The Arrhenius equation is

In k = − Ea/R × 1/T + A
[Gas constant, R = 8.31 J mol−1 K−1 and A is a constant]
2. What you want to do is use the equation and the data given at 700 to calculate a value for A.
So, you'd do ln(2.32x10^-3) = 184000/8.31 x 1/700 + A and rearrange that to calculate A.
Once you've got a value for A, write out the equation again, using the activation energy given, the value for A, and the temperature given. This will allow you to calculate lnk.
Once you have lnk, do e^lnk to find k (I'm not sure about this step but I think that's right).
It's a kind of strange question, took me a while to get my head around it.
3. So I did it and got something like 0.121 and I think its wrong. What did you get out of interest?

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Updated: July 27, 2017
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