What is Molecularity?

[Hammad Khan 2B]

From what I understand it’s just the number of reactants forming to a product. But I don’t think we went over moleuclarity as it applies to intermediate products. How would we calculate that?

[Sean Monji 2B]

More specifically, molecularity is the number of species that must collide for a step in the chemical reaction to proceed, not just the total amount of reactants forming a product. This tells us the rate of a step in a chemical reaction. or using the rate of the step in the reaction, we can find the molecularity.
For example, given the rate of the reaction is k[A], the molecularity is unimolecular, or if the rate is k[A]^2, that step must be bimolecular.
Hope that makes sense

[Sally Nason - 1K]

You can also think about molecularity in regards to the order of a reaction, as first order is unimolecular, second order is bimolecular, and third order is termolecular.

[Erica Nagase 1H]

Molecularity is the number of species/molecules that react in an elementary step. A unimolecular reaction (k[A]) involves 1 molecule (that reacts with the solution, container walls, photons, etc). A bimolecular reaction (k[A]²) involves 2 species/molecules colliding.

[Julia Cheng 2J]

Also, the greater the molecularity, the less likely the reaction is to happen since the probability of that many molecules colliding is less.

[JamesAntonios 1E]

I don't think that molecularity isn't involved in intermediates. Molecularity only applies to the reactants in the rate determining step. If there are intermediates in the slow step, you have to solve for correct pre-equilibrium rate law, I believe.

[Garret G 2F]

Here is a good video on the topic. It explicitly explains the difference between order and molecularity: https://youtu.be/qpoAb8rhUr0

[KayleeMcCord1F]

Is there a maximum molecularity that we'll deal with in this class?

[Arshpreet Sandhu 1B]

In lecture, Lavelle defined molecularity as the number of species in an elementary step. Molecularity of a reaction can be determined by the number of reactants (unimolecular, bimolecular, and termolecular.

[Sarah Clemens 1B]

Elementary rxns are classified according to their molecularity, the number of reactant molecules, atoms, or ions taking part in that particular rxn