The Behavior of Gases Part 1

The Properties of Gases  Kinetic energy –  The energy due to motion  What does temperature measure?  The average kinetic energy of the particles within a sample of matter. In a gas, the temperature (in Kelvin) is a way of indicating how fast the particles are moving.

Kinetic Theory Revisited  Assumption #1: Physical Properties of Gas Particles  Hard, spherical particles  Individual volumes are insignificant  Lots of empty space between the particles (this is why gases are so compressible)

Kinetic Theory Revisited  Assumption #2: Intermolecular forces  Gas particles are not attracted to each other – no intermolecular forces  Gases expand to the shape and volume of their containers

Kinetic Theory Revisited  Assumption #3: Particle movement  Random walks  Perfectly elastic collisions, which means there is no average kinetic energy loss over time

Variable Describing Gases VariableSymbolUnit

VariableSymbolUnit PressureP kPa or atm

Variable Describing Gases VariableSymbolUnit PressureP kPa or atm VolumeVL

Variable Describing Gases VariableSymbolUnit PressureP kPa or atm VolumeVL TemperatureT K (ALWAYS!)

Variable Describing Gases VariableSymbolUnit PressureP kPa or atm VolumeVL TemperatureTK Number of moles nmol

The Gas Laws  Boyle’s Law:  For a fixed mass of gas at constant temperature, the volume of the gas varies inversely with pressure

The Gas Laws  Example:  The pressure on 2.50 L of anesthetic gas changes from 105 kPa to 40.5 kPa. What will be the new volume if temperature remains constant? V1V1 P1P1 P2P2

The Gas Laws

 Charles’s Law:  The volume of a fixed mass of gas is directly proportional to its Kelvin temperature if the pressure is kept constant.

The Gas Laws  Example:  Exactly 5.00 L of air at -50 o C is warmed to 100 o C. What is the new volume if the pressure remains constant? V1V1 T 1 = = 223K T 2 = = 373K

The Gas Laws

 Gay-Lussac’s Law:  The pressure and Kelvin temperature of a fixed mass of a gas are directly proportional at constant volume.

The Gas Laws  Example:  The pressure of an automobile tire is 198 kPa at 27 o C. At the end of a trip on a hot sunny day, the pressure has risen to 225 kPa. Assuming the volume is constant, what is the new temperature? P1P1 T 1 = = 300K P2P2

The Gas Laws

 Combined Gas Law:  A relationship describing the behavior of gases that combines Boyle’s law, Charles’s Law, and Gay- Lussac’s law.

The Gas Laws  Example:  A gas at 155 kPa and 25 o C occupies a container with initial volume of 1.00 L. By changing the volume the pressure of the gas increases to 605 kPa as the temperature increases to 125 o C. What is the new volume?

The Gas Laws  Example:  A gas at 155 kPa and 25 o C occupies a container with initial volume of 1.00 L. By changing the volume the pressure of the gas increases to 605 kPa as the temperature increases to 125 o C. What is the new volume? V 1 = 1.00 L T 1 = 25 o C +273 = 298 K P 1 = 155 kPa

The Gas Laws  Example:  A gas at 155 kPa and 25 o C occupies a container with initial volume of 1.00 L. By changing the volume the pressure of the gas increases to 605 kPa as the temperature increases to 125 o C. What is the new volume? V 1 = 1.00 LV 2 = ? T 1 = 298 KT 2 = 398 K P 1 = 155 kPaP 2 = 605 kPa

The Gas Laws