## Homework 15.23

$\frac{d[R]}{dt}=-k[R]; \ln [R]=-kt + \ln [R]_{0}; t_{\frac{1}{2}}=\frac{0.693}{k}$

Sergio Alvarez 2L
Posts: 11
Joined: Fri Sep 25, 2015 3:00 am

### Homework 15.23

For part c, when trying to find [A]t, why do you subtract the value found from the mole ratio from 0.153, the value of [A]0?

Ronald Yang 2F
Posts: 86
Joined: Fri Sep 25, 2015 3:00 am

### Re: Homework 15.23

Because the amount that the concentration of B increases is essentially the amount that the concentration of A decreases (since you use up A to make B). Thus, you subtract the value you find with the mole ratio from the original amount of A to figure out the amount of A after that 115 seconds pass.