The
Clausius-Clapeyron relationship leads us
to the concept of relative humidity.
Relative
humidity is
defined as the ratio of the
amount of water vapor in the air to the amount
of water vapor that air would hold if it were
saturated. So completely saturated
air has
a relative humidity of 100%. If
the air has half
as much water vapor as it can hold, the relative
humidity is 50%.