Rate law??

Question

For a reaction aA--> products

[A]0= 5 M and the first two half lives are 25 and 50 minutes.

What is the rate law?

calculate k?

calculate [A] at t= 525 minutes

Answer 1

(a)

Step 1:

Initial concentration of A is .

First half life time is 25 min .

Second half life time is 50 min .

Observe that , each successive half–life is double the preceding one.

So the given reaction is second order reaction.

The rate law for second order reaction is .

Where k = rate constant ,

              [A] = concentration of A at time t.

Solution:

The rate law of reaction is .

Answer 2

(b)

Step 1:

Initial concentration of A is .

First half life time is 25 min .

Second half life time is 50 min .

Find the rate constant k .

Use the second order half life formula : .

Where k = rate constant ,

              [A]₀ = initial concentration of A .

Substitute and min .

Solution:

The rate constant is .

Answer 3

(c)

Step 1:

Initial concentration of A is .

First half life time is 25 min .

Second half life time is 50 min .

Find the  [A] at t = 525 min .

Use the second order Integrated rate law  : .

Where k = rate constant ,

            [A]₀ = initial concentration of A,

           t  is time.

Substitute , and min .

Solution:

The concentration at min  is .