GasesObjectives:

1. State the kinetic theory of matter.

2. Use the kinetic theory to explain states of matter

Review/Preview

What is kinetic energy? Kinetic Molecular Theory applies to gases.

What would “kinetic-molecular” theory logically discuss?

The Kinetic-Molecular Theory

Def.: describes the behavior of gases in terms of particles in motion

Kinetic-molecular theory makes several assumptions about the size, motion, and energy of gas particles.

Kinetic-Molecular Theory Basic Assumptions :

1. Size: Gases are made of small particles separated by A LOT of empty space. This means the volume of the particles is

negligible; assume volume = 0. Because particles are so far apart, there is no

significant attractive or repulsive force between them.

Kinetic-Molecular Theory Basic Assumptions :

2. Motion: Particles are in constant, random motion, moving in a straight line until they collide with something. They can collide with the container walls or

with each other. Collisions with each other are considered to be

elastic collisions: a collision in which no kinetic energy is lost (but it may be transferred).

Kinetic-Molecular Theory Basic Assumptions :

3. Energy: Kinetic energy is determined by a particle’s mass and velocity (KE = ½ mv2)

Since temperature is a measure of the average kinetic energy of the particles in a sample of matter, then temperature is directly proportional to average kinetic energy of a gas sample.

What happens to temperature if particles in a sample slow down?

Why?

Review

Complete Workbook (p.73): 1-4 together as a class.

Explaining the Behavior of Gases

1. Low density (What is density?) – lots of empty space between particles

2. Compression and expansion - stress ball demo

Explaining the Behavior of Gases, continued……..

3. Diffusion and effusion What is diffusion? Def: the movement of one material through

another (examples: perfume, blood gases) Particles move from areas of high concentration

to areas of low concentration Lighter (less mass) particles diffuse more

rapidly

Explaining the Behavior of Gases, continued……..

3. Diffusion and effusion, continued…. Effusion: when a gas escapes through a tiny

opening (think punctured tire) Inverse (??) relationship between effusion

rates and molar mass So which gas would effuse (escape) faster,

ammonia (NH3) or hydrogen chloride (HCl)?

Gas Pressure

Pressure: force per unit area (psi or N/m2) When gas particles collide with a container wall, they

exert force, creating pressure. Air pressure = column of air pushing down on the

ground. Why is air pressure lower at the top of a mountain than

it is at sea level? SI unit for pressure: pascal (Pa) = 1 N/m2

Others: 1 atm = 760 mm Hg = 760 torr = 101.3 kPa

Assignment

Workbook (p.73): 5-12 together Problem-Solving Lab (p.390)