15.29 b

[Annie Lieu-1H]

I got part a of this question without using the answer solution method by simple logistics (A decreases at 1/3 rate of B because of coefficients so subtract that from initial A) but part b requires we use that method and I don't understand it.

Why do we substract (1molA/2molB) in the first place for [A]T since I thought that only referred to A concentration...

and beyond that.


thank you.

[Brigitte Phung 1F]

So for part b) of this problem, we need to reuse the first-order integrated rate law again to solve for t. We need to convert from mols of B to mols of A and subtract this value from the initial A concentration to take into account how much A was used up to produce the 0.030 M concentration of B. This subtraction gives you the concentration of A at the time we're looking for! Hope this helps!