Unit IX Gas Laws
Be able to solve problems using the combined gas law (Boyle’s, Charles’,
GayLussac’s) and Dalton’s Law of Partial Pressure.
Be able to mass to volume or molarity to volume problems using the ideal
gas law or Avogadro’s principle with the combined gas law.
Know the implications of Graham’s Law of diffusion.
Be able to do stoichiometry with excess and limiting reactants.
Terms: ideal gas, STP, standard temperature, standard pressure, standard
conditions, diffusion, Avogadro’s Principle, molar volume, limiting reactant,
excess reactant, universal gas constant; Old Terms: molarity,
molar mass, reactants, products, emperical formula, percent, temperature,
pressure, moles, kinetic energy, potential energy.
Suggested Problems: Read Chapter 18 & 19
pgs 471-475 (27, 30-38, 40-47, 61, 65, 66) Review
pgs 494-497 (33-60) Review (1-5)
In this unit we will be using the ideas of kinetic theory of gases to calculate
amounts (stoichiometry) of gases involved in chemical reactions. In
past units we have learned how to calculate amounts of solids, liquids and
solutions by measuring mass and using molar mass (grams/mole) or knowing the
molarity (M, moles of solute/liter of solution). Because the denisty
of gases are so low it is difficult to measure the mass but it is reasonably
easy to measure the volume. Because the volume that a gas occupies is
dependent only on the number of particles (moles), the temperature and the
pressure (also easy to measure) we can determine the amounts of gases involved
in chemical reactions. (This only works well if the gas is not near
its boiling - some would call it condensation - point.)
In simpler terms, a student should be able to answer a question like: What
volume of air (at 28% oxygen by volume) at 23°C and 1 atmosphere of pressure
will it take to burn 125 grams of ethanol (one of the components of gasoline)?
To do these kinds of things the student will not only need to be able to
calculate amounts using gas laws (PV=nRT for example) but will also need to
write formulas, balance equations, calculate the number of moles from either
mass or volume and molarity.