Gas: Concepts

Properties of Gases Compressibility: how much the volume of matter decreases under pressure Gas compresses easily because the space between particles is large (gas particle volume is small compared to overall volume) Pressure: force exerted by the gas particles

How the Amount of Gas Affects Pressure Adding gas particles increases the number of collisions, which increases the pressure (in a closed container) Has a direct relationship (doubling the amount doubles the pressure) Gas particles move from areas of high concentration to low concentration If pressure inside a sealed container is lower than the outside air pressure, air will rush into the container If pressure inside a sealed container is higher than the outside air pressure, air will rush out of the container

How Volume Affects Pressure Reducing the volume of a container increases the pressure because there is less space for the particles to spread out, which causes more collisions Increasing volume decreases pressure Has an indirect relationship (when volume is doubled, pressure is halved)

Temperature Increasing temperature increases the kinetic energy of the particles, which makes them move faster and collide more often, so pressure is increased Decreasing temperature slows particles down, creating less pressure Has a direct relationship (doubling temperature doubles pressures)

Gas: Calculations (Basic)

Units Pressure: kilopascal (kPa, mmHg, atm) Volume: Liters (L) May need to convert from other units (use conversions provided on Reference Table!) Make sure units match! Volume: Liters (L) May need to convert from mL (divide by 1000) Temperature: Kelvin (K) May need to convert from Celsius (add 273)

Boyle’s Law At a constant temperature, the volume of a gas varies inversely with pressure P1V1 = P2V2

Charles’s Law At a constant pressure, volume of a gas is directly proportional to its Kelvin temperature =

Gay-Lussac’s Law At a constant volume, as the temperature of an enclosed gas increases the pressure increases =

Guided Practice Problem #1 A balloon contains 30.0 L of He gas at 103 kPa. What is the volume of the same gas when it rises in altitude to a pressure of 25.0 kPa?

Guided Practice Problem #2 A sample of nitrogen gas has a pressure of 6.58 kPa at 539 K. If the volume does not change, what will the pressure be at 211 K?

Guided Practice Problem #3 If a sample of gas occupies 6.80 L at 325°C, what will its volume be at 25°C?