Aim: What are the properties of Gases?

Compressibility•Compressibility is measure of how much volume decreases under increased pressure. • Gases are easily compressed because of the space between the particles in a gas. • The volume of the particles of the gas is small compared to the overall volume of the gas. • The distance between particles in a gas is much greater than the distance in the particles in a liquid or a solid. • Under increased pressure, the particles in a gas are forced closer together or compressed.

Factors Affecting Gas Pressure Four variables are used to describe a gas: 1. Pressure (P): kilo pascals 2. Volume (V): liters 3. Temperature (T): kelvin 4. Number of moles (n) • The amount of gas, the volume, and the temperature are factors that affect gas pressure.

Amount of Gas By adding gas into a container, you increase the amount of collisions on the walls of the container, increasing the pressure • If the container is rigid, the volume is constant and if the temperature is constant then the increase in pressure is proportional. If I double the number of particles, the pressure will double. • Aerosol cans:

Volume • You can increase pressure by decreasing volume • The more a gas is compressed, the more pressure the gas exerts. • By halving the volume, you double the pressure. • By doubling the volume, the pressure is halved. • Car pistons:

Temperature • As temperature increases, pressure increases. • Increasing average kinetic energy, increases the hits on the container wall and the amount of force on the wall which increases pressure. • As temperature doubles, pressure doubles • As temperature decreases, pressure decreases.

Gas Laws

Kinetic Molecular Theory (KMT) Kinetic molecular theory (KMT) for an ideal gas states that all gas particles: • are in random, constant, straight-line motion. • are separated by great distances relative to their size; the volume of the gas particles is considered negligible. • have no attractive forces between them. • have collisions that may result in a transfer of energy between gas particles, but the total energy of the system remains constant.

Boyle’s Law: Pressure-Volume Relationship

•The volume of a fixed mass of gas varies inversely with the pressure at constant temperature.•As the volume increases the pressure decreases.•As the volume decreases the pressure increases.•P1V1 = P2V2

•P1 = initial pressure P2 = final pressure•V1 = initial volume V2 = final volume

Practice – solve the following using Boyle’s law 1) A 4L balloon at 1 atm is released and the volume expands to 6L. Find the new pressure.

2) A 4L balloon at 101.3 kPa is placed under pressure of 202.6 kPa. Find the new volume.

Charle’s Law: Volume-Temperature Relationship

•The volume of a fixed mass of gas at constant pressure varies directly with the Kelvin temperature.•As the temperature increases the volume increases.•As the temperature decreases the volume decreases.• = •V1 = initial volume V2 = final volume•T1 = initial temperature T2 = final temperature

Practice – solve the following using Charles’s law 1) A 2L balloon at 300 K is heated to 750 K. Find the new volume.

2) A 4L balloon at 100°Cdeflates to 2L.

Find the new temperature.

Gay Lussac’s Law: Pressure-Temperature Relationship

•The pressure of a fixed mass of gas at constant volume varies directly with the Kelvin temperature.•As the temperature increases the pressure increases.•As the temperature decreases the pressure decreases.• = •P1 = initial pressure P2 = final pressure•T1 = initial temperature T2 = final temperature

Practice – solve the following using Gay-Lussac’s law 1) A gas at 202.6 kPa and 300 K is heated to 400 K. Find the new pressure.

2) A gas at STP is placed under a pressure of 3 atm. Find the new temperature.

Combined Gas Law•Boyle’s law, Charles’s law and Gay-Lussac’s law can be combined into a single law known as the combined gas law. The combined gas law states the relationship among pressure, volume and temperature of a fixed amount of gas.

• =

Practice – solve the following using the combined gas law

1) A 3L canister of gas is at 1.5 atm and 200 K. It is heated to 400 K causing the volume to increase to 7L. What is the new pressure?

2) A 1.5L balloon at STP

is placed under pressure of 148.4 kPa and temperature is lowered to 200 K. Find the new volume.

Deviations of Real Gases from Ideal Behavior A real gas:◦Does not behave completely according to the KMT.

◦Occupies space and exert attractive forces between on one another

Ideal Gas vs. Real GasLIKELY TO BEHAVE IDEAL Gases at high temperature and low pressure. Small nonpolar gas particle.

LIKELY TO NOT BEHAVE IDEAL Gases at low temperature and high pressure. Large polar gas molecules.