Order equations

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

nick_pantoja_3G
Posts: 25
Joined: Sat Jul 09, 2016 3:00 am

Order equations

What in a question tells you if a kinetic reaction is zero order, 1st order, or 2nd order?

Nikola_Stojcic_3O
Posts: 11
Joined: Wed Sep 21, 2016 2:55 pm

Re: Order equations

I think the question will state if it is a zero, first or second order reaction.

Eman_Burney_1D
Posts: 15
Joined: Wed Sep 21, 2016 2:57 pm

Re: Order equations

Graphically, if you see that the line has a negative slope (slope= -k), with time on the x-axis and ln[A] on the y-axis, this will tell you it is a first-order reaction. Additionally, rate= k[A] (differential rate law) signifies this as well, versus rate= k[A]^2 signifying a second-order reaction. Lastly, the unit that tells you if it is a first-order reaction is s^-1 (or 1/s). So for example, on page 117 of the course reader, question 4. of Quiz 2 Preparation is an example of a first-order reaction. In the question, it is stated that the straight line has a slope of -2.00 s^-1. So, since the unit used is s^-1, as well as the negative slope, we know it is a first-order reaction. A third way we could have known question 4 is a first-order reaction, is by the use of natural log in the problem (A plot of ln[NOBr] is stated in the problem). Natural log is seen in first-order reactions.

For second-order reactions, the unit used is 1/M*s, and has a positive slope with time on the x-axis and 1/[A] on the y-axis.

For zero-order reactions, the differential rate law is rate=k, and has a negative slope with time on the x-axis and [A] on the y-axis.

Hope this helped!