1. Kinetic Theory of Matter
Gases
Kinetic Theory of Matter

2. Kinetic Theory of Matter
Matter exists as solids, liquids & gases under normal conditions.
We can study the behavior of large groups of particles in all 3 states, but not individual particles

3. Review: Solids Definite shape Definite volume
Particles close together, fixed
Particles move very slowly
High density
Hard to expand/compress

4. Liquids Indefinite shape, definite volume Take the shape of container
Particles are close together, but mobile
Particles move slowly
High density
Hard to expand/compress

5. Gases Indefinite shape Indefinite volume
Take the shape and volume of container
Particles are far apart
Particles move fast
Low density
Easy to expand and compress

6. Kinetic Theory (late 19th century)
“Kinetic” from Greek kinetikos = moving
Based on idea that particles of matter are in constant motion---and this motion has consequences
Explains the properties of matter in terms of the energy the particles possess and the forces that act between them.

7. Kinetic Theory Model based on an ideal gas:
Imaginary gas that conforms perfectly to all of the assumptions of kinetic theory
Particles thought of as point masses with no volume or forces of attraction
A real gas can approach ideal behavior under conditions of high temperature and low pressure

8. Five Assumptions Gases consist of large numbers of tiny particles.
Volume occupied by a gas is 1000 times that of a liquid or solid of equal mass or number of particles.

9. Particles of a gas are in constant, random, rapid, straight-line motion and thus possess kinetic energy
The collisions between particles of a gas and between particles and the container walls are elastic collisions (no net loss of kinetic energy)

10. There are no forces of attraction or repulsion between the particles of a gas.

11. The average kinetic energy of the particles of a gas is directly proportional to the Kelvin temperature of the gas
K.E. = 1/2mv2
At absolute zero, all movement stops (no K.E.)

12. Maxwell Boltzman Distribution Scale
In a sample of gas, particles have the same mass, but are moving at different speeds.
The particles have varying amounts of energy, much like students during the passing periods in the halls

14. Change in conditions affects the distribution of particles

16. The Kinetic Theory explains a number of observed properties of gases

17. Expansion
Open valve
A gas has no definite shape or volume, but fills its container
Why?
Gas particles are independently moving in all directions, with no attraction or repulsion

18. Fluidity Ability of particles to flow, or glide past each other Why?
No attractive forces; particles in constant motion

19. Low Density
Gases are about 1000 times less dense than liquids or solids
Particles are much further apart---10 diameters apart

20. Compressibility Ability to reduce the volume of a sample of gas Why?
Great distance between particles results in lots of empty space. It is possible to crowd molecules closer together.

21. Diffusion Spontaneous mixing of two substances Why?
Particles are in random, constant motion; no forces of attraction

22. Effusion
Process by which gas particles under pressure pass through a small opening
Why?
Particles in constant motion; No forces of attraction

23. Deviations of Real Gases from Ideal Behavior
Why?
Particles do occupy space
Particles do exert attractive and repulsive forces upon each other

24. Greatest Deviations Low temperature and high pressure
Low temp→low K.E. →low velocity → particles feel attractive and repulsive forces
High pressure →closer contact → particles feel attractive and repulsive forces

25. Why do real gases approach ideal behavior at high temp and low pressure?
Greater speed
Particles far apart

26. Real gases vary in attractive forces
Noble gases & diatomics: very little
Polar gases (NH3, H2O): great attraction, therefore great variance from ideal behavior