Kinetics Units in Calculations

Based upon a rate equation for a reaction where:

rate = k [A]x [B]y
The order for the reaction is order = x + y

The units for rate are

mole * liter-1 * sec-1

Which could be written as:

liter * second

NOTE: the units may be given in a different form for concentration or for time. You should recognize the units (whatever they are) as being


From this, now we can discuss the units for (k) the rate constant.

For a 0 order reaction:

rate = k * [A]0
Since [A]0 = 1 and has no units
rate = k
and k has units mole * liter-1 * sec-1

For a first order reaction:

rate = k * [A]1
Since [A]1 = [A] with units mole liter-1
rate (mole * liter-1 * sec-1) = k * (mole liter-1)
so k has units sec-1

For a second order reaction:

rate = k * [A]2
Since [A]2 has units mole2 liter-2
rate(mole * liter-1 * sec-1) = k*(mole2 * liter-2)
so k has units liter * mole-1 * sec-1

Other Concentration Units:

Any concentrations units may be used for kinetics calculations. Don't forget that pressure is also a concentration unit.

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Last Updated 4/12/96