Exercise.
From the abundance table in Chapter 7, what are the concentrations
of H and He atoms in the entire universe, expressed in mole fractions?
Answer.
= 0.928
= 0.072
The other common concentration unit for gases is partial pressure,
.
In a mixture of gases, each gas molecule moves independently, and
every gas in the mixture behaves as if it were alone in the same
volume. In a mixture of gases, if one molecule out of every three
is a
moIecule, then the chlorine gas acts as if it alone occupied the
same volume with the same total number of
molecules, or one third the total pressure. If the total pressure
is 1 atm, then the partial pressure of
gas is one third of an atmosphere. In any gas mixture the partial
pressure of each component is its mole fraction times the total
pressure from all gases:
=
x
Thus oxygen gas in our atmosphere has a partial pressure of 0.20
atm and nitrogen gas has a partial pressure of 0.80 atm. The sum
of partial pressures of all components in a mixture must add to
give the total pressure of the mixture.