When to use each order


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205192823
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Joined: Wed Sep 18, 2019 12:19 am

When to use each order

Postby 205192823 » Sun Mar 15, 2020 6:49 am

How do I know when it’s zero, first, and second order?

VPatankar_2L
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Joined: Thu Jul 25, 2019 12:17 am
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Re: When to use each order

Postby VPatankar_2L » Sun Mar 15, 2020 6:56 am

You can tell the orders based on the graphs: for zero-order the graph of [A] vs time would be linear, for first-order the graph of lnA vs time would be linear, and for second-order the graph of 1/[A] vs time would be linear. You can also determine the order based on a data table by using experiment trials to determine the order for each reactant. You would look for the results in which the reactant whose order you are not calculating is being held constant while the reactant whose order you are trying to calculate is changing. You would compare the ratio of change in reactant concentration to the ratio of the rate to derive the order. Elementary steps of a reaction can also tell you the order of each reactant based on the coefficients.

Adam Kramer 1A
Posts: 103
Joined: Sat Aug 24, 2019 12:15 am

Re: When to use each order

Postby Adam Kramer 1A » Mon Mar 16, 2020 12:15 am

The order is the sum of the exponents in the rate law. You simply add them and whatever the sum is is the order of the reaction

Felicia Wei 1B
Posts: 48
Joined: Wed Nov 18, 2020 12:28 am

Re: When to use each order

Postby Felicia Wei 1B » Wed Mar 03, 2021 4:04 pm

Order is determined experimentally first. You can only find K once you have determined the order. In the lecture today Professor Lavelle went over how to identify this graphically. You want to look for the graph that will give you a straight line and that slope is K. Do this by graphing [A] vs t, ln[A] vs t, and/or 1/[A] vs t. Whichever one gives a straight line will determine if it is zero order, first order, or second-order(respectively).

Joseph_Armani_3K
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Joined: Wed Sep 30, 2020 9:58 pm

Re: When to use each order

Postby Joseph_Armani_3K » Wed Mar 03, 2021 4:43 pm

Algebraically, the order is the sum of the reactant concentrations' exponents. So if the rate = k[A][B], the reaction order would be 2 because 1+1=2

Graphically, the graph that is the most linear out of the three (A vs time, lnA vs time, 1/A vs time) is the reaction's order.


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