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order of reaction

Posted: Sat Mar 14, 2020 6:55 pm
How can you tell what the reaction order is?

Re: order of reaction

Posted: Sat Mar 14, 2020 7:01 pm
If there are two reactants, the order of a reaction is by adding up the two exponents in the rate law (rate = k[A]^n [B]^M, so the rate law is n + m). How do you find n and m? Usually they give you a bunch of experimental trials where they used different or same amounts of A and B to find different rates. Then you compare the different trials to find out the exponents (which finds the order or reaction) and find the rate constant (k). Dr. Lavelle did at least one practice question in lecture, so you can review that.

Re: order of reaction

Posted: Sat Mar 14, 2020 7:03 pm
This video is pretty good at explaining the concepts.

Re: order of reaction

Posted: Sat Mar 14, 2020 8:13 pm
This is a good video! I watched another of his videos on other general kinetics problems, and it was good.

Re: order of reaction

Posted: Sun Mar 15, 2020 4:55 am
You can also think of this graphically. I doubt we will ever be asked to do this by hand on a test, but if you graph the concentration [A]t vs time and you get a straight line, it is zeroth order. If you graph the natural log of the [A]t vs time and get a linear graph, it is first order. if you graph the reciprocal (1/[A]t) vs time and you get a straight line, it is second order.

Re: order of reaction

Posted: Sun Mar 15, 2020 5:18 am
I think the furthest we'll be tested on is the number of reactants.
Zeroth Order: $A\rightarrow A$
First Order: $AB\rightarrow A + B$
Second Order: $AB+CD\rightarrow AD+BC$
Third Order: $AB+CD+E\rightarrow AE+BC+D$

Re: order of reaction

Posted: Sun Mar 15, 2020 5:44 am
Within the scope of this class, we will be asked to find the order of reactions based on experimental data, which is the example with multiple experiments where the concentrations of each reactant varied between each experiment and this resulted in a differing rate of the overall reaction.