Hey guys,

Can anyone help me figure out how to do this question in the simplest terms possible??

Q: For the rxn: A + B ---> C, determine the order of the reaction with respect to B from the information given below. (I would of lined them up better but sdn wasn't letting me....sorry)

Initial [A]
2.5x10^-6
5x10^-6
1x10^-5

Initial [B]
3x10^-4
3x10^-4
9x10^-4

Rate
5x10^-3
1x10^-2
1.8x10^-1


Ok, so I know that you have to simplify and I know how to get the order with respect to A, but how do I get the rate with respect to B? After you simplify it...this is what it looks like:

line # [A] [B] [Rate]
1 1 1 1
2 2 1 2
3 4 3 36
4 1 3 9



Ok, so where did they pull line 4 from?? In the solution it says that for line 4, you have to look at lines 1 and 3 and see how much the rate changed for A and C, which is x4 and x36, respectively. Now your supposed to divide 36/4 to get 9. Then you take the rate change of [B] from line 1 to line 3 which is x3, and set up the formula:

3^x = 9
x = 2
so, this is the rate order of [B]

My main question is...when you divide 36/4 is the 36 and 4 found from the change from line 1 to 3 or are they just the numbers for the concentrations in line 3?

Same thing for 3^x = 9, do you get the (3) just by simply looking at [B] in line 3 or do you get it by finding the change of concentration from line 1 to line 3?

I know this is confusing, so tell me if I have to make my question more clear

Thanks a lot,

Hey guys,

Can anyone help me figure out how to do this question in the simplest terms possible??

Q: For the rxn: A + B ---> C, determine the order of the reaction with respect to B from the information given below. (I would of lined them up better but sdn wasn't letting me....sorry)

Initial [A]
2.5x10^-6
5x10^-6
1x10^-5

Initial [B]
3x10^-4
3x10^-4
9x10^-4

Rate
5x10^-3
1x10^-2
1.8x10^-1


Ok, so I know that you have to simplify and I know how to get the order with respect to A, but how do I get the rate with respect to B? After you simplify it...this is what it looks like:

line # [A] [B] [Rate]
1 1 1 1
2 2 1 2
3 4 3 36
4 1 3 9



Ok, so where did they pull line 4 from?? In the solution it says that for line 4, you have to look at lines 1 and 3 and see how much the rate changed for A and C, which is x4 and x36, respectively. Now your supposed to divide 36/4 to get 9. Then you take the rate change of [B] from line 1 to line 3 which is x3, and set up the formula:

3^x = 9
x = 2
so, this is the rate order of [B]

My main question is...when you divide 36/4 is the 36 and 4 found from the change from line 1 to 3 or are they just the numbers for the concentrations in line 3?

Same thing for 3^x = 9, do you get the (3) just by simply looking at [B] in line 3 or do you get it by finding the change of concentration from line 1 to line 3?

I know this is confusing, so tell me if I have to make my question more clear

Thanks a lot,


this was explained in a thread like an hour before this one by ajlst11.


So, when [A] doubles, and [B] is constant, the Rate ALSO doubles. Thats easy, 1st order. NOW, to get [B] you have to already account for [A] in this because there aren't two trials where [A] stays the same. So, from trials 2 to 3, [A] doubles and [B] triples. The rate is multiplied by 18. Automatically take in account the change in [A] and its effect on rate (it is 1st order so when it doubles so does the rate). This leaves us with the Rate being multiplied by 9 (the new rate from the effect of changing [A]0, now since [B] triples, and the Rate is multiplied by 9, this is 2nd order ((x)^2), just like before bc (3)^2=9. Let me know if this is right, I tried.


just extrapolate from 1 to 3 instead of 2 to 3 and you get your explanation.