## Quiz 2 Prep (#7 from Winter 2016)

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

Mihika Sridhar 3H
Posts: 11
Joined: Wed Sep 21, 2016 2:58 pm

### Quiz 2 Prep (#7 from Winter 2016)

I'm having some trouble understanding this question and the answer:
Q: Which one of the following is true for a reaction that has only one reactant?
A) If the reaction is first order, then t1/2 will double as the initial concentration of the reactant doubles.
B) If the reaction is zero order, then t1/2 will double as the initial concentration of the reactant doubles.
C) If the reaction is second order, then t1/2 will double as the initial concentration of the reactant doubles.
D) If the reaction is second order, then t1/2 will double as the initial concentration of the reactant is reduced to half.
E) Both B and D. [answer]

Ethan Frankel 2C
Posts: 20
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Quiz 2 Prep (#7 from Winter 2016)

Professor Lavelle derived half-life reaction laws during one lecture a week or so ago. On page 66 and 67 of the course reader, the half-life equations are provided: second order is t1/2 = 1/k[A]o and zero order is t1/2 = [A]o/2k. Since there's only one reactant, both zero order and second order reactions depend on initial concentration, whereas first order reactions depend only on k. Hope that helps!