The Gas State and Kinetic Molecular Theory (KMT)

Lesson 1Unit 5 Gases and Atmospheric Chemistry

Most substances can exist in the solid, liquid or gas states. Recall that the attractions between particles influence the state each substance is in at room temperature: 

The States of Matter

Ionic Compounds: contain strong electrostatic attractions and are therefore found in the solid state at room temperature. They have high boiling points (e.g. NaCl (s))

Polar Molecules: These compounds contain permanent dipoles and form strong dipole-dipole intermolecular bonds. They are found in the liquid or solid state but have a lower boiling point. (e.g. H2O (l))

Non-polar Molecules: These have no dipoles and contain very weak intermolecular bonds. They are usually gases. (e.g. H2 (g), Cl2 (g) , CO2 (g)).

The States of MatterGas, Liquid, and Solid - there is also a

fourth; it is called a plasma which has charged particles that can conduct electricity and are influenced by magnetic fields. It is similar to a gas in its properties

Vibrational Motion: back-and-forth motion of particles.

Rotational Motion: spinning motion of particles.

Translational Motion: straight-line motion from place to

place.

The Motion of Particles:

Phase Structure Movement of Particles

Shape and Volume

Ability to Pour

Compressibility

Solid - particles closely packed -particles in fixed positions

- vibration -definite shape -definite volume

-cannot be poured

-cannot be compressed significantly

Phase Structure Movement of Particles

Shape and Volume

Ability toPour

Compressibility

Liquid -particles closely packed -particles not fixed in position

-vibration -rotation -translation (slower)

- takes shape of container - Definite volume

-can be poured

- cannot be compressed significantly

Phase Structure Movement of Particles

Shape and Volume

Ability to Pour

Compressibility

Gas - particles widely spaced - particles not fixed in position

-vibration - rotation-translation (faster)

-occupies entire volume of container

- can be poured

- can be easily compressed

Kinetic Molecular Theory of Gases1. A gas consists of particles in constant,

random, straight-line motion; they collide with each other and with the walls of the container

2. Gas particles influence each other only by collision; they exert no other forces on each other.

3. All collisions between gas particles are perfectly elastic; all kinetic energy (energy of motion) is conserved.

4. The volume actually occupied by the particles of a gas is negligible; the vast majority of the volume of the gas is empty space through which the gas particles are moving.

5. Particles of different gases have equal kinetic energies at the same temperature.

Therefore, according to this theory, an ideal gas behaves much like billiard balls on a pool table.

Gas PressuresIn the KMT, pressure is the force exerted

against the wall of a container by the continual collision of molecules against it.  THE COLLAPSING CAN DEMO

HomeworkRead 416 – 422# 1, 2, 3 (a,b), 4, 5 on pg. 422.