M s1
s1
M1 s1
M2 s1
M3 s1
s1
M1 s1
M2 s1
M3 s1

M1 s1
Rates will normally have units of M s^1. So, the rate constant for a 2nd order reaction will have to have units M^1s^1 so that when multiplied by M^2, you end up with M s^1
Rates will normally have units of M s^1. So, the rate constant for a 2nd order reaction will have to have units M^1s^1 so that when multiplied by M^2, you end up with M s^1