PHYSICAL CHARACTERISTICS OF GASES

Chapter 10.1The Kinetic – Molecular Theory of Matter

Objectives:1. State the kinetic-molecular theory of matter,

and describe how it explains certain properties of matter.

2. List the five assumptions of the kinetic-molecular theory of gases. Define the terms ideal gas and real gas.

3. Describe each of the following characteristic properties of gases: expansion, density, fluidity, compressibility, diffusion, and effusion.

4. Describe the conditions under which a real gas deviates from “ideal” behavior.

Kinetic-Molecular Theory (KMT) Based on the idea that particles of

matter are always in motion. Provides a model of an ideal gas

Imaginary gas that perfectly fits all the assumptions of the kinetic-molecular theory.

KMT is based on the following 5 assumptions:

1. Gases consist of large numbers of particles that are far apart relative to their size.o Volume of gas particles occupy a volume

usually about a thousand times greater than liquid and solid particles.

•·       

2. Collisions between gas particles and between particles and container walls are elastic collisions.o Elastic collisions are ones in which there is

no net loss of kinetic energy.

3. Gas particles are in continuous, rapid, random motion. They therefore possess kinetic energy.o Kinetic energy is the energy of motion.

Animation

www.chm.davidson.edu/ChemistryApplets/KineticMolecularTheory/BasicConcepts.html

Source:

4. There are no forces of attraction or repulsion between gas particles.o Think of gas particles as small billiard balls,

when they collide , they do not stick together, they bounce apart immediately.

5. The average kinetic energy of gas particles depends on the temperature.o KE = ½ mv2

• m is mass of particle• v is it’s speed

Higher the temperature, the faster the particles move

Kinetic-molecular theory and the nature of gases

1. Expansion: Gases do not have definite shape nor volume The expand to fill container and take it’s

shape and volume

Kinetic-molecular

theoryGas particles move rapidly in all directions (assumption 3) without significant attraction or repulsion between them ( assumption 4)

2. Fluidity Ability to flow Liquids and gases are considered fluids

because they both flow

Kinetic-molecular

theory

3. Low Density Density of a gas is 1/1000th that of liquid or solids.

Kinetic-molecular

theoryParticles are so much farther apart in a gaseous state (assumption 1).

Animation

4. Compressibility Crowding particles closer together.

Kinetic-molecular

theoryGas particles are initially far apart (assumption 1), allowing the particles to be crowded together.

5. Diffusion Spontaneous mixing of the particles of two substances

caused by their random motion.

Kinetic-molecular

theoryRandom and continuous motion of the molecules (assumption 3) carries them throughout the available space.

6. Effusion Process by which gas particles pass through a tiny

opening.

Animation of Effusion

http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/gaslaw/micro_effusion.html

Source:

Deviation of Real Gases from Ideal Behavior Real Gas

Gas that does not behave completely according to the assumptions of the kinetic-molecular theory. There are actually attractive forces between

particles of gases, especially under higher pressures and lower temperature.

Kinetic-molecular theory Most likely holds true for:

Particles that have little attraction Ex: He, Ne ( monatomic and nonpolar) Ex: N2, H2 ( diatomic and nonpolar)

Gases more likely to deviate from ideal gas behavior Ex: NH3, H2O (Polar molecules) stronger

attractions