1. Physical Characteristics of Gases

2. TEKS Objectives
(9) The student understands the principles of ideal gas behavior, kinetic molecular theory, and the conditions that influence the behavior of gases. The student is expected to:
(C) describe the postulates of kinetic molecular theory
(A) describe and calculate the relations between volume, pressure, number of moles, and temperature for an ideal gas as described by Boyle's law, Charles' law, Avogadro's law, Dalton's law of partial pressure, and the ideal gas law
(B) perform stoichiometric calculations, including determination of mass and volume relationships between reactants and products for reactions involving gases; and

3. Kinetic-Molecular (K-M) Theory
All matter is made up of particles
The particles are constantly in motion
Explains the properties of solids, liquids and gases

4. Five Assumptions for Gases
Gases consist of large numbers of tiny particles that are very far apart
Collisions in gases are elastic (no loss of kinetic energy)
Particles are in continuous, rapid, random motion
No forces of attraction or repulsion between particles
Average kinetic energy depends on the temperature of the gas

5. Keep in mind…
At the same temperature, a gas’s kinetic energy is proportionate to its size
Small size < > Large
High temperature <------> Low
More energy < > Less
Ex: At the same temperature, hydrogen has more energy than oxygen

6. Physical Properties of Gases
1. Expansion: no definite shape or volume
2. Fluidity: particles glide past each other and behave as a fluid
3. Very low density
4. Compressibility: can physically change the volume

7. Physical Properties of Gases (continued)
5. Diffusion: spreading and mixing of gases depends on the speeds, diameters, and the attractive force between them
6. Effusion: the ability of a gas under pressure to pass through a small opening and is directly proportional to the velocity and mass of the gas

8. Celsius & Kelvin Conversions
When using gas laws, temperature must be in Kelvin
Absolute Zero is the theoretical temperature at which all kinetic energy stops
Kelvin (K) = Celsius (C°) + 273
Celsius (C°) = Kelvin (K) - 273

9. Four Properties Needed to Describe a Gas
1. Pressure
2. Volume: how much space it occupies
3. Temperature: a measure of the average kinetic energy
4. n = # of moles of gas ( 1 mole = x 1023 molecules)

10. Pressure
Definition: Force per unit area on a surface
(how much a specifically sized area is being pushed on)
SI unit for force is the Newton (N)

11. Gas molecules exert pressure on any surface they collide with
This pressure is determined by the temp, volume, and # of molecules present

12. Measuring Pressure/ Units of pressure
The atmosphere exerts pressure on the surface of the earth
Atmospheric pressure is measured by a barometer
A manometer is used to measure pressure in a container
At sea level, & zero Celsius, atmospheric pressure will support a column of mercury 760 mm tall
1 mm Hg also known as 1 torr

13. One atmosphere of pressure (atm) is defined as 760 mm of Hg
One pascal (Pa) is the pressure of one N acting on 1 square meter
Pa are usually expressed in kiloPascals (kPa)
kPa = 1atm = 760 mm Hg = 760 torr

14. STP
When comparing volumes of gases, you must know the temp and pressure (they affect volume)
For comparison, standard conditions for gases are needed
“Standard temperature and pressure” (STP)
STP is 1 atm of pressure and 0o C