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A2 chemistry kinetics

Hi, I'm struggling with this A2 chemistry question and was wondering if anyone could help? I understand how to find the order, but on this question there isn't a concentration the same of the H2, so I don't know how you would work out the order of NO. If I can find out the order I'd know where to go from there, I just can't get my head round it. If anyone could help with the method rather than just give me the answer I would really appreciate it.
Thanks

6. The data in the table below relates to the reaction between hydrogen and nitrogen monoxide at 673K. 2NO(g) + 2H2(g)  N2(g) + 2H2O(g)

. [No]. Rate
1. 2.0. 6.0 6.0
2. 3.0. 6.0. 9.0
3. 6.0. 1.0. 0.5

Deduce the rate equation and calculate the rate constant.

Reply 1

littleangel9914

Well you know the order of H2 so you have to factor in the affect of that on rate. So for example using trail 2 and 3 H2 conc is halfed as it has an order of one the rate should also half to 0.25 however it doesn't it increases by 36 times meaning the remaining affect on rate is due to the other reactant. Hope that make sense I can't put it into words properly :smile:

(edited 10 years ago)

Reply 2

Lifestalker

First, we must know if either of the products affect the rate of reaction. To do this, we look at the data presented:

|||||

. [No]. Rate
1. 2.0. 6.0 |||| 6.0
2. 3.0. 6.0. ||| 9.0
3. 6.0. 1.0. || 0.5

We see that, from 1 to 2, increasing the concentration of H₂ by 1.5 times (2.0 to 3.0) increases the rate of reaction 1.5 times (6.0 to 9.0). Therefore, we can deduce that H₂ is of order 1, in this reaction.

We do the same thing for NO. From 1 to 3, we see that the concentration of H₂ has been tripled, and we know it is order one, so we triple the rate of reaction (6.0 x 3 = 18.0). Now, we reduce the concentration of NO by 6 times. This brings the rate of reaction to 0.5.

If [NO] had been order one, the rate of reaction would have been reduced by 6 times too, so it would be 3. However, we know this not to be the case, as it is 0.5. So, what we do is...

We divide 18 by 0.5, which gets us 36.

So, by decreasing the concentration by 6 times, we get a reduction of the rate of reaction by 36 times. This means that [NO] is of order 2, as