Rate law Help?

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?

 

im a bit confused because the answer shows that it is a second order reaction but how do I tell the difference between zero first and second order reactions.

Answer 1

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 .