Chapter 14 The behavior of GAses 14.1 Properties of Gases

Compressibility Easily compressed Air bags in your car Compressibility A measure of how much the volume of matter decreases under pressure Why does a collision with an inflated air bag cause much less damage than a collision with a steering wheel or dashboard? Compression of molecules; absorbs the energy of the impact

Compressibility Why are the particles of gases easily compressed? Think about the kinetic molecular theory ****BECAUSE OF THE SPACE BETWEEN THE PARTICLES The volume of particles in a gas is small compared to the actual volume of the gas

Compressibility At room temperature, the distance between particles is about 10 the diameter of a particle.

Factors affecting gas pressure Remind me of the three assumptions of the kinetic molecular theory as they relate to the properties of gases. Four variables used to describe gases Pressure (kPa) Volume (L) Temperature (K) Number of moles (n) The amount of gas, volume, and temperature are the three factors that affect gas pressure

Amount of gas Kinetic theory can be used to predict and explain how gases will respond to a change of conditions Example: an air raft What happens when you inflate the air raft? Are you adding particles of gas? How is the pressure of the gas affected?

Assume constant temperature

Amount of Gas If the pressure of a gas in a sealed container is lower than the outside air pressure, what will happen when the container is opened? Causes the whoosh sound when a vacuum packed container is opened What happens if the gas pressure in a sealed container is higher than the outside pressure? Can you think of any examples?

Aerosol cans Pushing the spray button creates an opening to the lower pressure outside

Volume What happens to the pressure of a gas if volume is decreased? What will happen if the volume is doubled and the amount of gas remains the same? Assume constant temperature.

Temperature Why would a sealed bag of potato chips begin to bulge if the temperature is increased? Explain using the kinetic molecular theory?

Temperature Volume of container & amount of gas are constant Why would an aerosol can explode if thrown into a fire. What happens if the temperature of the gas decreases? Kelvin temperature!!!!

Boyle’s Law: Pressure and Volume Temperature is constant What type of relationship is this? The product of the two variables will be equal to a constant P1 x V1 = P2 x V2

Charles’s Law: Temperature and Volume Pressure and the amount of gas are constant relationship of the variables? The volume of a fixed mass of gas is directly proportional to its Kelvin temperature if the pressure is kept constant

Charles’s Law: Temperature and Volume The ratio of V/T is constant at all conditions of temperature and volume therefore V1/T1 = V2/T2 This is not true when the temperature is expressed in degrees Celsius. We must convert to Kelvin whenever solving gas law problems.

Gay-Lussac’s Law: Pressure and Temperature Volume is constant The pressure of a gas is directly proportional to the Kelvin temperature if the volume remains constant. At constant volume P1/T1 is equal to P2/T2 Therefore P1/T1 = P2/T2 What type of relationship is this?

The combined Gas law Describes the relationship among the pressure, temperature, and volume of an enclosed gas. Only the amount of gas (n) is constant 𝑃 1 𝑉 1 𝑇 1 = 𝑃 2 𝑉 2 𝑇 2