# Homework Help: Finding order of a reaction

1. May 20, 2013

### leroyjenkens

I've attached a screenshot of the internet page where the homework questions are, which shows the problem and my answers (It says I got A right, but B and C are wrong).

So I did this a few times with other tables and got the right answers, but this one is weird and the website isn't recognizing my answer.

So what I did was take the 3rd value of A, divided it by the 1st value of A and got 2 as the answer. I used those rows because A changes in those rows while B stays the same.

Then used the same rows to divide the 3rd row of the rate by the 1st row of the rate, and got 2 as my answer. 2 divided by 2 is 1, so the order is 1 for A. I got that one right.

Then I did the same thing with B. I divided the second row of B by the 1st row of B to get 1.666666667 as my answer. Then divided the second row of the rate by the 1st row of the rate to get 1. 1 divided by 1.66666667 = 0.6. It says that's wrong.

And the total order is 0.6 + 1, which is 1.6, which it says is wrong. The problem lies with the answer I got for B, but I don't know what I did wrong.
Maybe it has something to do with sig figs, but my calculator gives me an exact answer of 0.6.
Thanks.

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2. May 20, 2013

### Staff: Mentor

In general, it does not work like that - the division gives the correct result only in some special cases, or if the order is 1.

As you can see in row 1 and 2, the reaction rate does not depend on B at all. What does this tell you about the reaction order?

3. May 20, 2013

### leroyjenkens

Ohhhhh, of course. I didn't think about that. So that means the rate of the reaction is independent of the concentration of B, which means B is zero order. Thank you very much.