Gas Volumes and Ideal Gas Law
Up to this point, the gas laws have kept the amount of gas
(moles) the same.
Up to this point, the gas laws have kept the amount of gas
(moles) the same.
Law of combining volumes of gases
Up to this point, the gas laws have kept the amount of gas
(moles) the same.
Law of combining volumes of gases
At a constant temp and pressure, the volumes of gases in a
chemical equation are in a whole number ratio (same as the
coefficients)
Up to this point, the gas laws have kept the amount of gas
(moles) the same.
Law of combining volumes of gases
At a constant temp and pressure, the volumes of gases in a
chemical equation are in a whole number ratio (same as the
coefficients)
Ex : 3H2 + 2N2  2NH3
Up to this point, the gas laws have kept the amount of gas
(moles) the same.
Law of combining volumes of gases
At a constant temp and pressure, the volumes of gases in a
chemical equation are in a whole number ratio (same as the
coefficients)
Ex : 3H2 + 2N2  2NH3
3L of H2 + 2L of N2 = 2L of NH3
or
3mL of H2 + 2mL of N2 = 2mL of NH3
Avogadro’s Law
Avogadro’s Law
At a constant temp and pressure, equal volumes of gases
contain the same number of particles.
Avogadro’s Law
At a constant temp and pressure, equal volumes of gases
contain the same number of particles.
Ex: 3L of H2 will contain the same number of particles as
3L of O2. (as long as they are at the same temp and pressure)
Ex: At STP, 1 mole of an ideal gas = 22.4 L
The gases below are all at STP.
Why are their volumes all not 22.4 L?
Ideal Gas Law
Ideal Gas Law
This law combines Boyle’s, Charles’s, Gay-Lussac’s, and
Avogadro’s.
Ideal Gas Law
This law combines Boyle’s, Charles’s, Gay-Lussac’s, and
Avogadro’s.
R is a gas constant. The value depends on the units used in the
problem.
Example 1: What volume will 1.27 moles of helium occupy at
STP?
Example 2: Determine the number of moles of krypton
contained in a 3.25L gas tank at 5.80 atm and 25.5ºC.
Example 3: Determine the number of grams of carbon dioxide
in a 450.6mL tank at 1.80 atm and -50.5ºC.
Example 4: A 50.0L tank at -15ºC contains 14.00g of helium
and 10.00g of nitrogen. What is the pressure in the tank?
Example 5: What volume would 32.0g of NO2 gas occupy at
3.12 atm and 18.0 ºC?
Example 6: A 40.0g gas sample occupies 11.2 L at STP. What
is the molar mass of this gas?
Example 7: 1.089g of a gas occupies 4.50L at 20.5 ºC and
0.890 atm. What is its molar mass?
The ideal gas law can be used along with stoichiometry to
determine the volume or pressure of a gas in a chemical
reaction.
4C3H5(ONO2)3(l) -->12CO2(g) +10H20(g)+6N2(g)+O2(g)
If I know how many moles of gas are created, along with the
temperature and pressure, I can determine the volume.
Diffusion and Effusion
Graham’s Law of Effusion
Graham’s Law of Effusion
Predicts how fast one gas will effuse or diffuse compared to
another one.
Rate of effusion of A
Rate of effusion of B
√ MB
√ MA
Example 8: How many times faster would nitrogen diffuse than
oxygen?
Example 9: An elemental gas composed of diatomic
molecules diffuses at a rate 0.355 times that of oxygen.
What is the identity of the gas?
Gas Laws:
Dalton’s, Boyle’s, Charles’s, Gay-Lussac’s, Combined,
Avogadro’s, Ideal, and Graham’s
Common examples in everyday life and where these laws apply
Remember to subtract away the water vapor pressure when
collecting a gas over water
Use stoichiometry to predict volume, moles, etc. of gas from a
chemical equation (or vice versa)
STP = 1 atm and 0ºC
1 mole of gas at STP = 22.4L
Pressure = force/unit area
Convert between units of pressure
Remember all temperatures have to be in Kelvin (add 273 to Celsius)
Molar mass = grams of a substance per mole
Coefficients in a balanced equation of gases represent the volumes
Mole fraction in determining partial pressure or moles