### Stoichiometric Coefficient impact?

Posted: **Wed Feb 25, 2015 9:16 pm**

by **martha-1I**

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

### Re: Stoichiometric Coefficient impact?

Posted: **Wed Feb 25, 2015 10:30 pm**

by **Neil DSilva 1L**

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.