## Test 3 #8

$\frac{d[R]}{dt}=-k[R]^{2}; \frac{1}{[R]}=kt + \frac{1}{[R]_{0}}; t_{\frac{1}{2}}=\frac{1}{k[R]_{0}}$

Kelly Kiremidjian 1C
Posts: 62
Joined: Fri Sep 29, 2017 7:04 am

### Test 3 #8

8.) In a 2nd order reaction, a reactant has a known half-life of 3.00 minutes and an initial concentration of 5.00 M. How much time (in seconds) will it take for the concentration of this reactant to drop to 2.00 M?

Could someone explain how they did this question?

Qining Jin 1F
Posts: 53
Joined: Fri Sep 29, 2017 7:07 am

### Re: Test 3 #8

Since you have the half life and initial concentration, you can solve for k using the equation for second order half-life

t(1/2) = 1/(k[A]naught)

After solving for k, you can use the second order equation

1/[A] = kt + 1/[A]naught

Plug in 2.00M for [A], 5.00M for [A]naught, and k
then solve for t

RohanGupta1G
Posts: 34
Joined: Sat Jul 22, 2017 3:00 am

### Re: Test 3 #8

use the half life to solve for k and then use the integrated rate law.