The Behavior of Gases

Properties of Gases

• Compressibility: a measure of how much the volume of matter decreases under pressure.

• Gases are easily compressed because of the space between the particles. (remember KMT)

3 Factors Affecting Gas Pressure• 1. Amount of Gas: by adding gas you

increase the particles and number of collisions so the pressure increases, and vise versa.

• 2. Volume of Gas: by increasing the volume you increase the space that the particles can move in. Thus the pressure decreases as the number of collisions decreases, and vice versa.

• 3. Temperature: as the temperature increases the kinetic energy of the particles increases and they hit the walls of the container and each other with more energy, increasing the pressure, and vice versa.

Warm temp. Hot temp. Cold temp.

The Gas Laws• Boyle’s Law: If the temperature is

constant, as the pressure of a gas increases, the volume decreases.

P1V1 = P2V2

• 1) If I have 5.6 liters of gas in a piston at a pressure of 1.5 atm and compress the gas until its volume is 4.8 L, what will the new pressure inside the piston be?

• 2) I have added 15 L of air to a balloon at sea level (1.0 atm). If I take the balloon with me to Denver, where the air pressure is 0.85 atm, what will the new volume of the balloon be?

• 3) I’ve got a car with an internal volume of 12,000 L. If I drive my car into the river and it implodes, what will be the volume of the gas when the pressure goes from 1.0 atm to 1.4 atm?

• Charles Law: As the temperature of an enclosed gas increases, the volume increases, if the pressure is constant.

• When you use temperature in ANY gas law you must change the temperature into Kelvin

• Kelvin = ºC + 273

• Find the volume of 250 mL of a gas at 25 °C if the temperature is dropped to 10 °C.

• Gay-Lussac’s Law: As the temperature of an enclosed gas increases, the pressure increases, if the volume is constant.

• Calculate the final pressure inside a scuba tank after it cools from 1.00 x 103 °C to 25.0 °C. The initial pressure in the tank is 130.0 atm.

• The Combined Gas Law: all three gas laws combined.

• Convert 250 mL of a gas at 50 °C and 650 mm Hg to STP

• A gas starts at 1 atm, 30 °C and 1 L. What is the final temperature if the final amounts are 5 atm and 0.5 L.

• Ideal Gas Law: includes the number of particles (n= moles) and the ideal gas constant (related to pressure).

• 1 mole = 6.02 x 1023 particles

• R = (22.4 L x 1 atm/1 mol x 273 K)

= 0.0821 L x atm/mol x K

• How many moles of a gas will you have if 1 liter of gas is collected 28.0 °C and 1.7 atmospheres pressure.

• R = (22.4 L x 760 mmHg/1 mol x 273 K) = 62.4 L x mmHg/mol x K

• R = (22.4 L x 1 atm/1 mol x 273 K) = 0.0821 L x atm/mol x K

• R = (22.4 L x 101.3 kPa/1 mol x 273 K) = 8.31 L x kPa/mol x K