First order and second order reaction rates


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Cesar P
Posts: 3
Joined: Tue Nov 25, 2014 3:00 am

First order and second order reaction rates

Postby Cesar P » Sat Mar 14, 2015 3:18 pm

How do we tell the difference between first order and second order ?

Neil DSilva 1L
Posts: 70
Joined: Fri Sep 26, 2014 2:02 pm

Re: First order and second order reaction rates

Postby Neil DSilva 1L » Sat Mar 14, 2015 3:33 pm

When you're looking at a rate law, a first order reaction will have an overall order of one (the sum of all the exponents will be 1) and a second order reaction will have an overall order of 2 (the sum of all the exponents will be 2).

The exponents can be determined experimentally (for reactions with multiple reactants), by looking at the graphs of the natural log of the concentration vs. time (first order) or the reciprocal of the concentration vs. time (second order) and determining which one produces a straight line (for a single reactant reaction).

Another way to determine the order of the reaction is to look at the units of the k value (rate constant). For a first order reaction, k will have units of second-1 and for a second order reaction, k will have units of L.mole-1.second-1.

Chem_Mod
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Re: First order and second order reaction rates

Postby Chem_Mod » Sat Mar 14, 2015 7:51 pm

Neil is correct.

104607508
Posts: 23
Joined: Fri Sep 25, 2015 3:00 am

Re: First order and second order reaction rates

Postby 104607508 » Sat Feb 13, 2016 5:14 pm

how can we tell when a reaction will have a fractional rate order? is it when the products decompose into the reactants?


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