Molecularity

[Payton Kammerer 2B]

I'm a little confused on the definition of molecularity. Or I suppose, the definition of "species"
Is a species a single molecule, or is it a single type of molecule? I may be confused because in biology, a species is a type of organism, but this definition seems to have little to do with that. In an elementary step in which two NO molecules collide, is that one or two species?

[Brian_Ho_2B]

Molecularity accounts for both the number of different types of species as well as their stoichiometric coefficients. For instance, if an elementary step had something like: 2A + B --> something, the molecularity is termolecular, because in total, there are three molecules involved.

[Justin Sarquiz 2F]

A species in this case refers to the number of reactants. In the example you gave, this is bimolecular. The number of moles of reactants determines the molecularity.

[Robin Cadd 1D]

The textbook defines molecularity as the number of reactant moles, atoms, or ions taking part in a specified elementary reaction.

[Christineg1G]

Molecularity would be the number of molecules or species in an elementary step, and also determine the rate. Rate law for each elementary steps comes directly from molecularity.