Experimental rate reaction questions

[Golaso]

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Hi everyone,

I came up yesterday to a question while doing Kaplan practice exams dealing with the rate reaction; so if anyone can explain to me an easy way in figuring out how to do such questions:

1) Trial [A]o (M) o (M) rate (M/min)
1 x 10–2 3 x 10–3 2 x 10–3
1 x 10–2 6 x 10–3 8 x 10–3
2 x 10–2 1.2 x 10–2 3.2 x 10–2
What is the reaction order with respect to A?
A. 1
B. 1.5
C. 2
D. 3
E. 0
answer is E

2)
Initial [A] (M) Initial (M)Initial rate of formation of C(mol/L•min)
2.5 x 10–6 3 x 10–4 5 x 10–3
5 x 10–6 3 x 10–4 1 x 10–2
1 x 10–5 9 x 10–4 1.8 x 10–1
A. zero order
B. first order
C. second order
D. third order
E. fourth order
Answer is C

Thanks for your time

 

[RalphMouth]

The easiest way is to compare 2 rate values at which only one concentration changes.

In problem one, we can easily see that comparing the first experiment to the second, the concentration of B is doubled, while the overall rate is quadrapuled. Therefore, B is second order. (2^2)

Comparing experiment 1 to 3, we see that concentration B has quadrupled and the rate has increased 16 times. This is consistent (4^2) with our prior results. However, we also see Concentration A has doubled, but there was no effect on the overall rate. That is, only what we expected from B to effect the rate happened. Therefore, A has no effect on the rate and has a order of 0.

What is the question for problem 2?

 

[RalphMouth]

Actually, you can do the problem without the actual question.

For problem 2, we can figure out comparing experiment 1 to 2 that the order for A is 1. Concentration of A doubles, rate of reaction doubles.

Again, we compare experiment 1 to 3. Concentration of A quadruples, so if nothing else changes the rate should have increased 4 times (1st order 4^1). However the actual rate has changed 36 times. Therefore, B affected the rate 9 times. The concentration of B was tripled. Therefore B is second order ( 3 ^2). I assume the question was what is the order of B.

 

[Golaso]

The easiest way is to compare 2 rate values at which only one concentration changes.

In problem one, we can easily see that comparing the first experiment to the second, the concentration of B is doubled, while the overall rate is quadrapuled. Therefore, B is second order. (2^2)

Comparing experiment 1 to 3, we see that concentration B has quadrupled and the rate has increased 16 times. This is consistent (4^2) with our prior results. However, we also see Concentration A has doubled, but there was no effect on the overall rate. That is, only what we expected from B to effect the rate happened. Therefore, A has no effect on the rate and has a order of 0.

What is the question for problem 2?

sorry, I forgot to write the question, my bad:
For the reaction: A + B → C, determine the order of the
reaction with respect to B from the information given
below.