Question

Exp. CO(atm) O2(atm) Rate (atm/s)

1	2.2	1	0.121
2	1.1	1	0.03025
3	1.5	1.5	0.084375

What is the reaction order of O2?

Answer 1

In order to calculate the rate law expression for a A+B reaction, we need to apply Initial Rates Method.

Note that the generic formula goes as follows:

r = k [A]^a [B]^b

Note that if we got at least 3 sets of point, in which we have A and B constant, then we could use:

r1 / r2 = (k1 [A]1^a [B]1^b) / (k2 [A]2^a [B]2^b)

If we assume K1 and K2 are constant, then K1= K2 cancel each other

r1 / r2 = ([A]1^a [B]1^b) / ( [A]2^a [B]2^b)

Then, order according to [A] and [B]

r1 / r2 = ([A]1/[A2])^a * ([B]1/[B]2)^b

If we get two points in which A1 = A2, then we could get B, and vise versa for A...

From the data shown in YOUR table

choose point 1 and 2, so O2 cancels

0.121/0.03025 = (2.2/1.1)^a * ( 1/1)^b

4 = 2^a

a = 2

now,

choose point 2 and 3

0.03025 / 0.084375 = (1.1/1.5)^a * (1/1.5)^b

0.35851 = 0.7333^2 * (0.66667)^b

0.35851 / ( 0.7333^2) =  (0.66667)^b

0.6667=  (0.66667)^b

b = 1

this is 1st order with respect to O2