Page 1 of 1

### 7B 3(c)

Posted: Sat Mar 14, 2020 6:15 pm
Determine the rate constant for each of the following first order reactions, in each case expressed for the rate of loss of A:
(c) 2A --> B + C, given that [A]0 = 0.153 mol/L and that after 115 s the concentration of B rises to 0.034 mol/L.

I was able to do parts (a) and (b) for this problem, but I'm not sure how to approach part (c)

### Re: 7B 3(c)

Posted: Sat Mar 14, 2020 7:32 pm
I am also slightly confused by this question, but what I think is happening is that we are given an initial concentration of A as 0.153 M, and then we use the information that after 115s, there is 0.024 mol B. Since B is a product, we had to have used some of the A to form B, so we have to subtract what was used to form B from the initial concentration of A, which yields 0.085 molA. We then use this value of the [A]t in the equation k=ln([A]o/[A]t)/t.

### Re: 7B 3(c)

Posted: Sun Mar 15, 2020 4:37 am
Since .034M of product B was created, than (according to the stoichiometric coefficients) we can assume that 2(.034M) of reactant A was consumed.
We then subtract .153(initial concentration of A) - 2(.034M) = .085M
.085M = [A]t