Unit 10
Gases
Units 6-9 described what we know about matter on a very small scale: electrons, atoms, ions, and molecules. In the last four units of Chemistry 217 (Units 10-13), we move to collections of atoms and molecules, and describe how bulk matter behaves in its different phases. Unit 10 is about gases. There are a number of gas laws that describe quantitatively how ideal gases behave in terms of pressure, volume, and temperature. This unit also covers gas effusion and diffusion and the behaviour of “real” gases.
Objectives
After completing this unit, you should be able to
- describe the general characteristics of gases, and compare them to the characteristics of liquids and solids.
- interconvert the units of pressure: kilopascal, atmosphere, torr, and
mm Hg.
- state Boyle’s Law, Charles’s Law, and Avogadro’s Law.
- solve problems involving the variables pressure, volume, number of moles, and temperature using the ideal-gas law or the related laws (Boyle’s Law, Charles’s Law, and Avogadro’s Law).
- relate the density of a gas to its molar mass, pressure, volume, and temperature, and solve problems involving these quantities.
- solve problems involving partial pressures and mole fractions of nonreacting gas mixtures.
- perform calculations involving the collection of gases over water.
- list the statements that summarize the kinetic-molecular theory of gases, and use these statements to explain the ideal-gas law and related laws.
- sketch a graph to show how molecular speeds depend on temperature.
- predict and explain the effect of a change in one of the following variables of a gas sample on the other variables: volume, pressure, number of molecules, temperature, average kinetic energy of the molecules, average speed of the molecules, and number of collisions of the molecules with each other or with the walls of the container.
- solve problems involving Graham’s Law.
- explain how the mean free path of molecules affects the rate of diffusion.
- list the two factors that cause departures from ideal-gas behaviour for real gases, and explain the effect of these factors on the ratio PV/RT for real gases.
- explain the correction factors a and b that appear in the van der Waals equation for a real gas.