# 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.