Agenda

• Behavior of Gases• Gas Laws• Gas Laws Worksheet

Closed System

A closed system does not

exchange matter with its

surroundings but energy can

come and go as it pleases.

Kinetic Molecular Theory

Empirical (based on

experiments) description of

gases that the gas laws are

based on.

Collisions of Gas Particles

Kinetic Molecular Theory

Kinetic Molecular Theory

Postulate (Assumption) 1

Gases consist of tiny particles

(atoms or molecules)

Kinetic Molecular Theory

Postulate (Assumption) 2These particles are so small, compared with the distances between them, that the volume (size) of the individual particles can be assumed to be negligible (zero).

Kinetic Molecular Theory

Postulate (Assumption) 3The particles are in constant random motion, colliding with the walls ofthe container. These collisions with the walls cause the pressure exertedby the gas.

Kinetic Molecular Theory

Postulate (Assumption) 4The particles are assumed not to attract or to repel each other.

Kinetic Molecular Theory

Postulate (Assumption) 5The average kinetic energy of the gas particles is directly proportional to the temperature of the gas

Ideal GasesParticles in an ideal gas…

have no volume.have elastic collisions. (When they collide no energy is lost)are in constant, random, straight-line motion.don’t attract or repel each other.have an avg. KE directly related to Kelvin temperature.

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Real GasesParticles in a REAL gas…

have their own volumeattract each other

Gas behavior is most ideal…at low pressuresat high temperaturesin nonpolar atoms/molecules

Kinetic Molecular TheoryGases expand to fill any container.

random motion, no attraction

Gases are fluids (like liquids).

no attraction

Gases have very low densities.

no volume = lots of empty space

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Gas Variables

žFour variables to describe a gas:

Pressure (P)Volume (V)Temperature (T)Amount (n)

Ideal Gas Relationships

As Pressure Increases, Temperature IncreasesBy extension – As Pressure Decreases Temperature Decreases

As Volume Increases, Temperature AND Pressure DecreaseBy extension – As Volume Decreases, Temperature and Pressure Increase

As Amount (number of moles) Increases, Pressure and Temperature Increase

By extension – As Amount Decreases, Pressure and Temperature Decrease

In a Closed System…

Gas Law Apparatus

Air Valve

Temperature Sensor

Pressure Gauge

Air Volume