Initial Rate Law Question - Equation giving strange answer

[Xedfed]

Hi there, I was wondering if someone could give me hand with this question. I understand the basics of initial rate law and 0, 1st and 2nd order however the equations I use are giving strange answers to this particular question. For example, my answer for k was 0.0422347714, is this correct? Here is the question:

 

Q: Consider the reaction P_​4 ​+ 6H _​2==> 4PH_​3

A rate study of this reaction was conducted at 298K. The data that were obtained are shown in the table:

 

[P4] mol/L [H2] mol/L Initial Rate mol/L.s

 

0.0110 0.0075 0.000320

0.0110 0.0150 0.000640

0.0220 0.0150 0.000639

 

a) What is the order with respect to P4 and H2?

b) Write the rate law for this reaction

c) Determine the value and units of the rate constant, k

 

Cheers!

 

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Edited May 14, 2017 by Xedfed

[Country Boy]

I know very little about chemistry but, as a mathematician, my first thought would be to fit a power equation, in x, the concentration of P4, and y, the concentration of H2, to this:

 

rate= C x^ny^m. The three data points give three equations to solve for m, n, and C.

 

0.000320= C(0.0110^n)(0.0075^m)

0.000640= C(0.0110^n)(0.0150^m)

0.000639= C(0.0220^n)(0.0150^m)

 

If I am reading this correctly, m is the "order" with respect to P4 and n is the "order" with respect to H2.

[studiot]

I make k = 0/0427, pretty close to your figure.

 

I make the rate equation

 

Rate = k[H₂] ie independent of [P]

 

from the supplied data.

 

I have to admit that I know little about the reactions between Phosphorus and Hydrogen but I would guess that the reason this appears to be a first order reaction is that it is a multistep reaction with the initial dissociation of H₂ molecules as the rate determining step.

Edited May 15, 2017 by studiot