Gases: The Ideal Gas
Law Combination of the three empirical gas laws, (Boyle's, Charles', and Avogadro's) described in the preceding three sections leads to the ideal gas law which is usually written as: |
PV = nRT |
where P = pressure, V = volume, n = moles, T = kelvin temperature
and R. |
The constant R in this equation is known as the universal
gas constant. It arises from a combination of the proportionality constants
in the three empirical gas laws. The universal gas constant has a value
which depends only upon the units in which the pressure and volume are measured.
The best available value of the universal gas constant is: |
8.3143510 J/mol K or
8.3143510 kPa dm^{3}/mol K |
Another value which is sometimes convenient is 0.08206 dm^{3}
atm/mol K. |
This equation is used to determine molecular mass from gas
data. |
Example: A liquid can be decomposed by electricity into
two gases. In one experiment, one of the gases was collected.
The sample had a mass of 1.090 g, a volume of 850 mL, a pressure of 746
torr, and a temperature of 25^{o}C. Calculate its molecular
mass. |
To calculate the molecular mass we need the number of grams
and the number of moles. We can get the number of grams directly from
the information in the question. We can calculate the moles from the rest
of the information and the ideal gas equation. |
V = 850 mL = 0.850
L = 0.850 dm^{3} P = 746 torr/760 torr = 0.982 atm T = 25.0^{o}C + 273.15 = 298.15 K PV = nRT molecular mass = g/mol = 1.090 g/ 0.0341 mol = 31.96 g/mol.
The gas is oxygen. Go to the Ideal Gas Worksheet |
Go to the Gas
Law Review |