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:

mole ---------------- 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

Concentration ---------------- time

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.

This page is maintained by Scott Van Bramer

Please send any comments, corrections, or suggetions to svanbram@science.widener.edu.

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Last Updated 4/12/96