SL Chem - Unit #3: Kinetic Molecular Theory

State of Matter:

The attraction between particles using intramolecular forces influences the state of the substance at room temperature

Ionic Compound at room temp

Solid at room temp

• Strong electrostatic attraction

Polar Molecules at room temp

Solid or Liquid at room temp

• Permanent dipoles and have strong dipole-dipole bonds

Non-Polar Molecules at room temp

Mainly a Gas at room temp

• No dipoles so it’s very weak

Why do states change occur when energy is added?

This is because the energy adds kinetic energy to the particles (motions)

• So add energy to a solid and it makes a liquid add energy to a liquid it forms a gas

Why are state changes not a chemical change?

Because the chemical composition remains the same and the only thing changing is it’s physical composition

Solids

• Vibrational motion from kinetic energy

• Fixed volume and shape

• Strong attraction forces between particles leading to smaller spaces between them

• Incompressible with a low degree of disorder

Transition between solid and liquid

Melting

• Intermolecular bonds are weakened

Liquids

• Increased vibrational and rotational motion

• Fixed volume but a variable shape

• Weaker attraction between particles but still has small spaces between particles

• Incompressible but with a moderate degree of disorder

Transition between liquid and gas

Boiling

• intermolecular bonds are broken

Gasses

• Increased vibrations, rotation, and translational motion

• Variable volume and shape

• Very weak attraction between particles with large spaces between particles

• Compressible and with a high degree of disorder (randomness)

Vibrational Motion

A slight movement of atoms within a molecule/lattice structure

• Normally in solids, but are in all states

Rotational Motion

The rotation of molecules which makes them change positions

• Normally in liquids and gasses, not in solids

Translational Motion

Particles that move from one place to another in a straight line

• Only in glasses

Kinetic Molecular Theory of Gases: Describing an ideal gas

1. Individual gas particles have no volume compared to the space between its particles. 

2. The gas has no attractive or repulsive forces exist between the particles in a gas

3. Gas particles move constantly and randomly with a distribution of speeds. (They have a very high translational energy and move randomly in a straight line)

4. Collisions of the molecules with each other or the walls of the vessel are elastic. (no loss of kinetic energy)

5. The average kinetic energy of a gas is directly related to temperature. (The greater the temperature, the greater the kinetic energy)

When do real gases behave like ideal gases?

At high temperatures and low pressures

• When particles start to get further apart and force and the volume become insignificant