Units for k

[VanessaZhu2L]

Can someone explain how to find the units of k? Does each order always have the same units or do we need to calculate it for each problem? Thank you!

[JonathanM]

So each order of reaction has the same units of k because the end units must always come out to M/s. So for example for a zero order reaction, the units are M/s since nothing else is multiplying k. For first order reactions the units of k are 1/s since a concentration is being multiplied in once, so in the end you get M/s. For second order reactions the units are 1/(s*M) since there are two concentrations being multiplied by K. This logic continues for any order reaction.

[connie ma 3G]

basically the units for k must ensure that the units for the resulting rate is always M/s. so if it is zero order overall then the units for k have to be M/s because rate=k. if it is first order then the units for k will be 1/s because rate=k[A] where [A] already has units of M so k only needs to add the 1/s for the units of rate to be M/s when multiplied.

[RylanPurificacion 3J]

If you wanted a equation for it, the units would be in 1/(M^z-1*s), where z is the order for the reaction.

[derickngo3d]

Units for the rate constant should cancel with the units of molarity, so that the rate constant is in molar per second.
Hope this helps!

[derickngo3d]

You can either memorize or just mathematically calculate the units too!
Hope this helps!

[Joyce Pang 2H]

you could always just set up the equation for rate, but in units instead-- so since rate is M/s, and equation for first order would be M/s=k*M, and solving for k would leaev you with 1/s=k, etc. etc.

[RyanKopeikin_2I]

To be honest I just look at the right side of the equation and figure out how to make it match the left side of the equation, which is usually in units of M/s. So if it's a second order rxn, you have M/s = k (M)(M) so you can kinda figure out that the units of k need to be M^-1•s^-1

[rhettfarmer-3H]

I think Mathew gave us the cheat code for K units. So rate = k a to a power. So Zero is m/s. One is 1/s and second is 1/sm.

[Armen_Isayan_2L]

Hello! In order to find the units of k, you must consider that each order of reaction contains the same units of k. This is because the unit utilized in the end must be M/s. For instance, in a zero-order reaction the ultimate unit would be M/s, and this is due to the fact that no other units are multiplied to k. Also, for first-order reactions, the unit of k would be 1/s, and this is because it is being multiplied. Finally, in a second-order reaction, the unit of k is 1/(M*s), because there are two concentrations being multiplied to k.

[Shana Patel 1C]

You can memorize or calculate it.
Rate = k a to a power. So Zero is m/s. One is 1/s and second is 1/sm.

[Alan Nguyen 2I]

The units for K depend on the order of the reaction. This can be determined by keeping in mind that the rate is given in M/s. Use this to think about what units the existing terms on the other side of the equation have, and then think about cancelling units to find out what the units for K are.