States of Matter Podcast 1
Chapter 12.1
Gases
Chapter Vocabulary
• Kinetic molecular theory• Elastic collision• Temperature• Diffusion• Effusion• Pressure• Barometer• Pascal• Atmosphere• Dalton’s Law of Partial
Pressures
• Intermolecular forces (review)
• Viscosity• Surface tension• Surfactant• Cohesion• Adhesion• Melting point/boiling point• Vaporization• Evaporation• Vapor pressure
Kinetic Molecular Theory
Kinetic Energy
KE = ½ m v2
Temperature:
Pressure
P = F/A
Gas pressure results from gas particles colliding with the container
The more collisions and the more energy for each collision, the higher the pressure
Barometer
Manometer
Units of Pressure
Movement of Gas Molecules
Diffusion
Effusion
Graham’s Law of Effusion
Graham’s Law of Effusion
=
Balloons are made of rubber, which is porous enough for some gas particles to escape over time.
Q: Which balloon would go flat the fastest; a balloon filled with helium or a balloon filled with air?
Practice Problem 1
In an experiment, nitrogen gas effuses at a rate of 25 mol/s and an unknown gas effuses at 50 mol/s. What is the molar mass of the unknown gas?
Practice Problem 2
It takes 3.5 minutes for a sample of Xe to effuse. A different unknown gas takes only 1.2 minutes to effuse. What is the molar mass of the unknown gas?
Dalton’s Law of Partial Pressures
Sample Problem 3In a mixture of O2, CO2, and N2, the total pressure is found
to be 205 kPa. If CO2 has a partial pressure of 55 kPa and N2 has a partial pressure of 125 kPa in the mixture, what is the partial pressure of the oxygen gas?
Sample Problem 4
Air is a mixture of 78% N2, 21% O2, 1% Ar, and trace amounts of other gases. If the total pressure is 760 mmHg, find the partial pressure of each gas.
Mole Fraction
For a mixture of gases:
XA = nA / nT
Derived from Daltons’ Law of Partial Pressures
PA = XA * PT
number of molA
total number of mol
The partial pressure of one gas in a mixture is equal to the ratio of gas molecules in the mixture x the total pressure
X PTPA =
Sample Problem 556 g of N2 gas are mixed with 128 g of O2 g at a
total pressure of 1.5 atm.
a)What is the mole fraction of N2?
b)What is the partial pressure of N2?