How to use general rate laws to find rates of specific equations?

[ashwathinair]

How do you use rate laws to find the rate of a specific reaction? For example, in 7C 1:
Each of the following is an elementary reaction. Write its rate law and state its molecularity. (a) NO + NO --> N2O2; (b) Cl2 --> Cl + Cl.

[JamieVu_2C]

Since these are elementary reactions, you can write the rate law using the coefficients. For part a, since there are 2 NO molecules on the reactant side, the rate = k[NO]^2, and it is bimolecular. For part b, there is only 1 Cl2 molecule, so the rate = k[Cl2], and it is unimolecular.

[Daria MacAuslan 1H]

Rate laws can be used in this question because for bimolecular reactions like the one in part a, the rate is simply equal to k[NO}^2, because there are two molecules of NO reacting and colliding with each other. This makes the coefficient for NO 2, and thus that becomes the exponent in the rate law (since this is an elementary reaction). In the second one, the rate can be just written as rate=k[Cl2] since it is unimolecular.

[ashwathinair]

Rate laws can be used in this question because for bimolecular reactions like the one in part a, the rate is simply equal to k[NO}^2, because there are two molecules of NO reacting and colliding with each other. This makes the coefficient for NO 2, and thus that becomes the exponent in the rate law (since this is an elementary reaction). In the second one, the rate can be just written as rate=k[Cl2] since it is unimolecular.

Wait, but I thought order is independent of stoichiometric coefficients?

[ashwathinair]

Wait never mind, I found the unimolecular/bimolecular info in my notes! Thanks!