Gay-Lussac’s Law
 Pressure and temperature relationship
 Pressure results from molecular collisions
 Pressure of gas is DIRECTLY proportional to temperature.
 P , T 
 P , T 
 P1 = P2
T1 = T2
SOOO
 P1T2 = P2T1
 Remember to keep units the same. Temperature MUST be in
Kelvin
Example 1:
 A coke can has 5.00atm of gas at 21°C. Calculate the
pressure inside the can when it is found in a warehouse
during the summer at 38°C.
Example 2:
 The pressure of my tires before a road trip to Wyoming
was 1.5atm at 25°C. After returning to North Carolina,
my tire pressure is 1.7atm. What is the temperature (in
°C) outside?
Example 3:
 A gas sample in a closed container with a temperature
of 100°C and a pressure of 3.00atm is heated to 300°C.
What is the pressure of the gas at this elevated
temperature?
Avogadro’s Law
 Volume of a gas is DIRECTLY proportional to # of gas
particles (moles of gas)
 Temperature and Pressure are held constant
 V1 = V2
n1 = n2
  # gas particles,  volume
  # gas particles,  volume
 Ex. Blowing up a balloon
Dalton’s Law of Partial
Pressures
 Pressure of each gas DIRECTLY proportional to
amount of moles of a gas
 Increase gas particles, increase pressure
 Decrease gas particles, decrease pressure
 Partial pressure—
 Pressure of one gas that contributes to the total
pressure in a mixture of gases
 Total mixture pressure--- The sum of the individual gas pressures in a mixture
Dalton’s Law of Partial
Pressures
 Total Pressure (PT) of gas mixture =
 Sum of partial pressures of each gas in the mixture
PT = P1 + P2 + P3
Example 1:
 Calculate the partial pressure (in mmHg) exerted by
the 4 main gases in air at 760 mmHg: nitrogen, oxygen,
argon, and carbon dioxide. Their abundance by
volume is 78.08%, 20.95%, 0.934%, and 0.035%
respectively.
Water Displacement with
Dalton’s Law
 How do we collect and measure gases? Water
displacement
 Gas displaces water but the gas is mixed with water
vapor
 Application of Dalton’s Law allows the adjustment for
the amount of water vapor to be made so just the
amount of gas collected can be measured.
Water Displacement with
Dalton’s Law (cont.)
 Water vapor is mixed in with gas of interest so need
to separate.
 PT = Pgas + Pwater
 look up vapor pressure of water at different
temperatures
Example 2:
 A sample of nitrogen gas is collected over water at a
temperature of 23.0°C. What is the pressure of the
nitrogen gas if atmospheric pressure is 785 mmHg?
Example 3:
 A student has stored 100.0 ml of neon gas over water
on a day when the temperature was 27.0°C. If the
barometer in the room reads 743.3 mmHg, what is the
pressure of the neon gas in the container?
Homework
 Gay-Lussac’s Worksheet #1, 3, 5, 7, 10
 Dalton Worksheet