What are the rate of reaction units?
For any reaction? Concentration per unit time.
What units of time do you want? Seconds? Minutes? Hours? Well, whatever you can measure with a stopwatch I suppose... Know what makes sense given the numerical value of the rate you are looking at. Is it about the picosecond-time-scale autoionization of water? The 10-second time-scale of the reaction of crystal violet with sodium hydroxide? The billions-of-years-time-scale of the uranium-238 decay chain?
What unit of concentration do you want? Molecules per unit volume? Molarity? Your choice... depends on whether you are a statistical mechanical chemist or a more typical experimentalist.
The rate of reaction is given as
#r(t) = k[A]^m[B]^n#
#= -1/a(Delta[A])/(Deltat) = -1/b (Delta[B])/(Deltat) = 1/c(Delta[C])/(Deltat) = 1/d(Delta[D])/(Deltat)#
for the reaction
#aA + bB -> cC + dD#
#k#is the rate constant (constant with respect to temperature).
#[" "]#is the concentration of a given reactant.
#m#is the order of reactant #A#.
And we know that
being the slope of a concentration vs. time plot, the units are clearly