Quiz 2 Preparation

$aR \to bP, Rate = -\frac{1}{a} \frac{d[R]}{dt} = \frac{1}{b}\frac{d[P]}{dt}$

Elnaz Guivatchian 3L
Posts: 11
Joined: Wed Sep 21, 2016 2:55 pm

Quiz 2 Preparation

Can someone please explain number 10 from the practice quiz in the course reader
Thanks

Geoffrey Zhang 3I
Posts: 26
Joined: Wed Sep 21, 2016 3:00 pm

Re: Quiz 2 Preparation

You have to use the integrated rate law for second order reactions. After plugging the values in, you will see that the time it takes are different. I used 1/[A]subscript t = 1/[A]0 + kt

Alex Dib 4H
Posts: 34
Joined: Wed Sep 21, 2016 2:57 pm

Re: Quiz 2 Preparation

We know its a second order reaction because of the exponent given in the rate law; rate = k[A]2

Using the integrated rate law for second order reactions, we can rearrange the equation and solve for time. Knowing that k is the same constant at both initial concentrations, we can ignore it. This gives t=1/[A]-1/[A]0. When plugging in initial and final concentrations for both 1.0M-->0.50M and 0.50M-->0.25M, we get different times, showing us that half life depends on initial concentration for second order reactions.