1. Learning Goal: I will be able to… … solve gas problems using the ideal gas law or any other gas law.

2. Combined gas law: PV/T = k Boyle’s Law PV = k (at constant T and n)
A. The Ideal Gas Law
Combined gas law: PV/T = k
Boyle’s Law PV = k (at constant T and n)
Charles’s Law V/T = b (at constant P and n)
Avogadro’s Law V/n = a (at constant T and P)
Volume depends on T, P, and n: V = R(Tn/P)
Combining and rearranging the equation gives the
ideal gas law:
PV = nRT
universal gas constant R = L atm/K mol
units must be P in atm, V in L, T in K

3. The Ideal Gas Law
Most gases obey this equation closely / behave ideally at pressures of ~1 atm or lower, and ~0oC or higher.
You should assume ideal gas behavior when working your chemistry problems.
This equation can be used to solve all types of gas law problems:
List the initial and final conditions of the gas
If needed, convert P to atm, V to L, T to K
Rearrange the equation so that the quantities that change are on one side and the quantities that remain constant are on the other side; this will simplify the equation: ex.: you may end up with Boyle’s equation or Charles’ equation

4. Example: Initial Conditions Final Conditions
P1 = atm P2 = atm
V1 = 3.48 L V2 = ?
T1 = 258 oK T2 = 309 oK (oK = oC + 273)
Notice that n is not given, but we know it has not changed.
PV = nRT should be rearranged as:
Change Constant
PV = nR T
which leads to P1V1 = nR = P2V2 and P1V1 = P2V2
T T T T2
Solving for V2 will give us the answer:
V2 = P1V1 T2 = L
T1P2

5. C. Gas Stoichiometry (covered before)
Molar Volume
Standard temperature and pressure (STP)
0oC and 1 atm
For one mole of a gas at STP
Molar volume of an ideal gas at STP = 22.4 L
Mole-mole ratio = liter-liter ratio for gases

6. B. Dalton’s Law of Partial Pressures
What happens to the pressure of a gas as we mix different gases in the container?
For a mixtures of gases in a container, the total pressure exerted is the sum of the partial pressures of the gases present.
Ptotal = P1 + P2 + P3
The pressure of the gas is affected by the number of particles
The pressure is independent of the nature of the particles

7. B. Dalton’s Law of Partial Pressures
Therefore:
The volume of the individual particles is not very important.
The forces among the particles must not be very important.

8. B. Dalton’s Law of Partial Pressures (not in notes)
Collecting a gas over water
Total pressure is the pressure of the gas + the vapor pressure of the water.

9. B. Dalton’s Law of Partial Pressures (not in notes)
Collecting a gas over water
How can we find the pressure of the gas collected alone?

10. B. The Kinetic Molecular Theory of Gases
13.3
B. The Kinetic Molecular Theory of Gases

11. 13.3
D. Real Gases
Gases do not behave ideally under conditions of high pressure and low temperature. Why?
At high pressure the volume is decreased
Molecule volumes become important
Attractions become important (London disp. forces)