## Molecularity and rate laws

$K = \frac{k_{forward}}{k_{reverse}}$

Giselle Littleton 1F
Posts: 78
Joined: Wed Sep 18, 2019 12:20 am

### Molecularity and rate laws

How is molecularity related to the order of a reaction rate law?

Ryan 1K
Posts: 101
Joined: Fri Aug 09, 2019 12:15 am

### Re: Molecularity and rate laws

A unimolecular elementary step corresponds to a first order rate law. A bimolecular elementary step corresponds to a second order rate law, and so on and so on. As such, they are directly correlated with each other and can be used interchangeably to describe a reaction.

Aliya Jain 2B
Posts: 101
Joined: Wed Sep 11, 2019 12:16 am

### Re: Molecularity and rate laws

I think that if something is unimolecular, the order of the reaction would be one. similarly, if something is bimolecular, the order of the reaction would be two.

Niharika 1H
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Joined: Thu Jul 25, 2019 12:16 am

### Re: Molecularity and rate laws

Molecularity corresponds directly to the order of the reaction. (unimolecular = 1, bimolecular = 2, etc)

Frank He 4G
Posts: 50
Joined: Tue Nov 12, 2019 12:19 am

### Re: Molecularity and rate laws

Ryan 1K wrote:A unimolecular elementary step corresponds to a first order rate law. A bimolecular elementary step corresponds to a second order rate law, and so on and so on. As such, they are directly correlated with each other and can be used interchangeably to describe a reaction.

Is there a good reason why we don't just simplify the naming and call them the same thing?

Ryan 1K
Posts: 101
Joined: Fri Aug 09, 2019 12:15 am

### Re: Molecularity and rate laws

Frank He 4G wrote:
Ryan 1K wrote:A unimolecular elementary step corresponds to a first order rate law. A bimolecular elementary step corresponds to a second order rate law, and so on and so on. As such, they are directly correlated with each other and can be used interchangeably to describe a reaction.

Is there a good reason why we don't just simplify the naming and call them the same thing?

I think it has to do with the fact that even though they are highly related, order has to do with the concentrations of the reactants (since it's applied to the rate law), whereas the molecularity has to do with the number of molecules.