### Reaction Order

Posted:

**Sun Mar 10, 2019 4:51 pm**How do we know if a reaction is first/second order? and What does it mean for a reaction to be first/second order?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=145&t=43982

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Posted: **Sun Mar 10, 2019 4:51 pm**

How do we know if a reaction is first/second order? and What does it mean for a reaction to be first/second order?

Posted: **Sun Mar 10, 2019 5:23 pm**

It depends on the sum of all exponents in the rate law. The rate law can only be calculated experimentally.

Posted: **Sun Mar 10, 2019 6:15 pm**

It depends on the exponents

Posted: **Sun Mar 10, 2019 6:19 pm**

A reaction would be first-order if the exponents on the elements in the rate law add up to 1. Likewise, the reaction would be second-order if the exponents on the elements in the rate law add up to 2.

Posted: **Sun Mar 10, 2019 6:39 pm**

We can determine if a reaction is first or second order using the equation rate = k[A]^n[B]^m. If n and m add up to one, it is a first order reaction. If n and m add to two, it is a second order reaction. Also, if a reaction is first order, then the graph of ln[A] vs t will have a slope of -k. If a reaction is second order, then the graph of 1/[A] vs t will have a slope of k. Hope this helps!

Posted: **Wed Mar 13, 2019 1:03 pm**

Thank you!