## Difference between zero, first, second [ENDORSED]

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

Nicole Jacobs 1C
Posts: 59
Joined: Thu Jul 13, 2017 3:00 am

### Difference between zero, first, second

What is the difference between the zero, first, and second reactions? i still dont really get it

Lucian1F
Posts: 87
Joined: Fri Sep 29, 2017 7:07 am
Been upvoted: 1 time

### Re: Difference between zero, first, second

Let's say we have a reaction A -> B. For zero order reactants, the rate at which the reaction occurs is not affected by the concentration of that reactant. So if [A] is 1.0M in one reaction but [A] is 2.0M in another reaction, the rate at which the reaction occurs will be the same for both concentrations of A.

For first order reactants, the rate at which the reaction occurs is related to the concentration of the reactant to the first power. So if [A] is 1.0M in one reaction and 2.0 M in another reaction, the rate at which the reaction occurs in the reaction with 2.0M of A is double that of the rate of the reaction with 1.0M of A. This is because the concentration of A doubled, and 2 to the first power is 2, so the rate increases by a factor of 2.

For second order reactants, the rate at which the reaction occurs is related to the concentration of the reactant to the second power. So if [A] is 1.0M in one reaction and 2.0M in another reaction, the rate at which the reaction occurs in the reaction with 2.0M of A is quadruple that of the rate of the reaction with 1.0M of A. This is because the concentration of A doubled, and 2 to the second power is 4, so the rate increases by a factor of 4.

104922499 1F
Posts: 53
Joined: Fri Sep 29, 2017 7:04 am

### Re: Difference between zero, first, second

First Order
slope = -k
n=1
-d[A]/dt = k[A]^1
ln[A] = -kt

Second Order
slope = k
n=2
-d[A]/dt = k[A]^2
1/[A] = kt + (1/[A])0

Zero Order
Slope = -k
n=0
-d[A]/dt = k
[A] = -kt

Masih Tazhibi 2I
Posts: 33
Joined: Fri Sep 29, 2017 7:06 am

### Re: Difference between zero, first, second  [ENDORSED]

Lucian did a fantastic job explaining the rate orders here. I would also like to add that experimentally, you determine rate orders by isolating the impact of one reactant at a time on the overall reaction rate. If you have two reactants, you would keep one constant and change the concentration of the other, and vice versa. This becomes important when given a list of data with different variations in reactant concentration, because it allows you to reason out which data sets to pick.