* DEALS WITH A MIXTURE OF
DIFFERENT GASES *
1.) The sum of the
pressures of the individual gases equals the total pressure exerted by the
mixture of gases.
PTOTAL = Pgas1 + Pgas2 + ...
EXAMPLE: A mixture
of oxygen and nitrogen exerts 1.1 atm of
pressure. What is oxygen's partial pressure if the pressure of the
nitrogen gas is 0.8 atm?
2.) The pressure of a gas "collected over water" is equal to
the atmospheric pressure minus the vapor pressure of the water.
Pgas = Patm
- Pwater
EXAMPLE: A 44.6 mL sample of carbon dioxide is collected over water at 765
mm Hg pressure and 25 oC. What is
the vapor pressure of the "dry" gas? (The vapor pressure of
water at 25 oC is 23.76 mm Hg. You
will have to look up this value on a table or this value must be given to you.)
3.) The partial
pressure of a gas is equal to the "mole fraction" multiplied by the
total pressure.
Px = (moles
x) . Ptotal
“Px“ = partial pressure of certain gas
(total moles)
* "mole
fraction" = (moles x)
(total moles)
EXAMPLE: A mixture
of gases contains 2.0 moles of He and 4.0 moles of
oxygen. If the mixture exerts a pressure of 801 torr,
what is the partial pressure of the oxygen?
Link to the Dalton's Law and Graham's Law
Worksheet