deciding which order

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Jose Torres
Posts: 31
Joined: Fri Sep 28, 2018 12:22 am

deciding which order

Postby Jose Torres » Wed Mar 06, 2019 9:31 pm

How do we determine whether we are dealing with a first, second, or zero order reaction? Any easy hints in questions or chemical equations?

Andrea Zheng 1H
Posts: 61
Joined: Fri Sep 28, 2018 12:26 am

Re: deciding which order

Postby Andrea Zheng 1H » Thu Mar 07, 2019 12:03 am

If you are given the units of K, you can determine the order of the reaction by looking at those units, as they should cancel out with the reactant's units to get , which is the unit for the rate of the reaction. You know that the [reactant] is .

For example:
Rate constant (k) for a reaction has units . Using the equation {rate = k*[reactant]^order}, this means that = *[]^order. For this, the sec on both sides would cancel out, leaving you with = []^order, meaning it is 1st order.
Last edited by Andrea Zheng 1H on Thu Mar 07, 2019 12:05 am, edited 1 time in total.

Lia Inadomi 1I
Posts: 62
Joined: Fri Sep 28, 2018 12:15 am

Re: deciding which order

Postby Lia Inadomi 1I » Thu Mar 07, 2019 12:04 am

It depends on what information you're given in the problem. If they give you initial concentrations and initial rate values often you are able to determine how concentration effects rate to find out that way. If they only give you time and initial concentration then you can use the linear plots to determine. And if they give you the rate constant you can find the overall order based on the units. Hope this helps!

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