Proper Units for the rate constant

[Sean Phen]

How do you identify the proper units for the rat constant, k, for each reaction order?

[Lea Baskin Monk 1F]

If I can't remember, I use the rate law to solve for the unit. For example, if the reaction is second order rate = k[reactant]^2. The unit for the reactant is M and the unit for rate is M/S (or any unit of time) so only way to cancel out the M^2 is for the unit of k to be 1/MS

[Edgar Velazquez 2K]

Other than working through an equation to find the correct units, the easiest way is probably to just memorize them. Zero order units are M/s. First order units are 1/s. Second order units are 1/Ms.

[Queena Chu 3E]

I think the easiest way is to memorize them. We have only done 0-2 second order so it’s not a lot.

[Alyson Chou 3H]

The units for the rate constant are determined by the overall order of the reaction. For zero order, the units are M/s. For first order, the units are 1/s. For second order, the units are 1/M*s.

[AbenaaMensahBonsu2F]

Like other people have said, if I forget I use the units associated with the concentrations to find the k units. The k units have to cancel out the M valus so its left with reciprocal seconds. When in doubt, I just use that method.

[Caitlin Beale 3E]

The units of the rate constant, k, depend on the overall order of the reaction. The overall order of a reaction is the sum of the orders with respect to each reactant.

For a zero-order reaction, the rate is independent of the concentration of the reactant. Therefore, the units of k are given by the units of concentration per unit time, or M/s.

For a first-order reaction, the rate is proportional to the concentration of the reactant. Therefore, the units of k are given by the inverse of time, or 1/s.

For a second-order reaction, the rate is proportional to the square of the concentration of the reactant. Therefore, the units of k are given by the inverse of concentration times time, or 1/Ms.

[Natalie Hurd 1H]

To find units, I solve for k units so I do not have to memorize. The rate of a reaction is always M/s and the rate of each reactants is M. So using this you can solve for k. For example: rate = k[A]^2[B] -> M/s = k[M]^2[M] -> M/s = kM^3 -> k = 1/M^2*s

[Freddie P-G 1H]

You can either remember it or solve for it mathematically:
Remember: Zero order= M S-1
First order: S-1
2nd order: M-1 S-1
3rd order: M-2 S-1 etc.

Or: Do rate / [X] (there could be more [] of other species) and solve via cancellation

[Dashrit_Pandher_1J]

For the most part the units of the rate constant remains the same within in each reaction order, but if you are ever confused, just solve the rate law for k only looking at the units. Since 0 order means the reactant has no effect on the rate, it makes sense that k and the rate have the same units. Also from the 2nd order and on, M in the denominator is raised to the power of the order minus 1. For example, for the 3rd order, k = 1/M^2 *s ; 3-1=2 which is the exponent M is raised to.

[Anabelle Pham 2C]

The units depend on the overall order of the reaction. So, for a zero-order reaction, it is M/s. For a first-order reaction, it is 1/s. For a second-order reaction, it is 1/Ms.