## Order of a Reaction

$aR \to bP, Rate = -\frac{1}{a} \frac{d[R]}{dt} = \frac{1}{b}\frac{d[P]}{dt}$

EllaBerry
Posts: 68
Joined: Fri Sep 28, 2018 12:29 am

### Order of a Reaction

Why would a reaction involving [A][B] creating some product [P] not necessarily be a second order reaction even though two different molecules must collide for the reaction to occur? Is a reaction only second order if the concentration of the reactants are raised to the power of 2?

Christopher Tran 1J
Posts: 77
Joined: Fri Sep 28, 2018 12:15 am

### Re: Order of a Reaction

A reaction involving [A][B] is not necessarily a second order reaction since the rate of the reaction might not be dependent on the concentration of one of the reactants (such as when they're already in excess compared to the other reactant).

The sum of the powers of the reactant concentrations have to add up to two in the rate law equation for the reaction to be second order.

Danny Elias Dis 1E
Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

### Re: Order of a Reaction

To add to the previous answer, if a reaction rate is not dependent on the concentration of a certain reactant, that means it is to the power 0. This, along with the fact that [A] and [B] can be to technically any power, means [A][B] is not necessarily second order.

Eric Quach 1C
Posts: 30
Joined: Fri Sep 28, 2018 12:20 am

### Re: Order of a Reaction

Adding on to the answers, to find the order one must plot the ln A, one over A, and just A (A being concentration of a reactant) against time to determine if it is first, second, or zero order. For the overall order, add the orders of each reactant to get the order for the entire reaction.