Determining the rate law from experimental data

[fridakahlo]

Homework Statement

First question on PDF:
http://ars-chemia.net/Classes/102/Problem_Sets/Practice Exam for Exam 1 Key.pdf

Homework Equations

I used the initial rates method:
Rate2/Rate1=k2*[A]^m/k1*[A]^m

The Attempt at a Solution

When I solve these types of problems with the initial rates method, I get multiple possible solutions. For instance, for reactant B, I got -2.5 when comparing rates 3 and 2, but when comparing rates 3 and 1 I got -0.5. I know the answer is -0.5.
My question is how do I know which one is the most plausible answer when solving these types of problems?

 

[epenguin]

It was rather hard for me to make out what your question is. I guess it is about Question 1? This appears to be solved correctly, I presume the answers in red are yours? What is written above though does not correspond to this answer.

 

[Dr Uma Sharma]

Homework Statement

First question on PDF:
http://ars-chemia.net/Classes/102/Problem_Sets/Practice Exam for Exam 1 Key.pdf

Homework Equations

I used the initial rates method:
Rate2/Rate1=k2*[A]^m/k1*[A]^m

The Attempt at a Solution

When I solve these types of problems with the initial rates method, I get multiple possible solutions. For instance, for reactant B, I got -2.5 when comparing rates 3 and 2, but when comparing rates 3 and 1 I got -0.5. I know the answer is -0.5.
My question is how do I know which one is the most plausible answer when solving these types of problems?

you take any ratio ...answer should be same
If you take R1/R3 then [A] is canceled and if you do R3 and R1 then plug in the conc of A with raise to power of its order .. it should give us the same answer ...