## Stoichiometric Coefficient impact?

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

martha-1I
Posts: 76
Joined: Fri Sep 26, 2014 2:02 pm

### Stoichiometric Coefficient impact?

Does the Stoichiometric Coefficient have an impact on how I should approach a first order reaction problem asking me to solve for k given that the concentration of A decreases to 1/4 its initial concentration in 61 minutes?
Reaction: 2A ---> B + C
this is from question 14.24

Neil DSilva 1L
Posts: 70
Joined: Fri Sep 26, 2014 2:02 pm

### Re: Stoichiometric Coefficient impact?

No, I believe the stoichiometric coefficients wouldn't change anything in regards to the half-life. For first order reactions, the half-life is only dependent on k (t = ln2 / k). So if we're given the time, that's all we need to solve the problem.

To go from 1 whole quantity to half that quantity takes one half-life, then to go from half a quantity to a quarter of the quantity is another half life. So the total time we're given is equivalent to two half-lives. So one half-life is 30.5 minutes. Then you can use the half life equation and solve for k.