## 15.23 c

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

sofiakavanaugh
Posts: 58
Joined: Thu Jul 13, 2017 3:00 am
Been upvoted: 1 time

### 15.23 c

Hi,

I have tried to look at other people's answers for this question but for some reason I still don't understand what is happening conceptually: to find [A]t given an increase in [B], why do you have to do [A]o-[B]xmolA?

Thanks

Cristina Sarmiento 1E
Posts: 52
Joined: Wed Nov 16, 2016 3:02 am

### Re: 15.23 c

The equation given is 2A --> B + C
So there is a decrease in A because it is making B (an increase in B)
If we know the increase in B, we can use the coefficients from the equation to convert moles of B back to moles of A.
The number we get from the conversion is how much A was used to make B. So if we subtract this number from the initial [A], we can get [A]t.

Hope this makes sense.