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?