# 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 mole^{2} liter^{-2}
rate(mole * liter^{-1} * sec^{-1}) = k*(mole^{2} * 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