The Kinetic Molecular Theory

The Kinetic Molecular

TheoryMovement in solids, liquids, and gases

The theory of moving molecules!

• Describes the differences between gas, liquid, and solid states.

Assumptions within the KMT

• 1. Gases are made of tiny particles that are far apart from each other.

• 2. Gas particles are in continuous, rapid, random motion

More Assumptions• 3. There are no attractive forces between

molecules under normal conditions.• 4. Collisions between particles are elastic (no

energy is lost due to friction).

Last Assumption• 5. Particles at the same temperature have the

same average kinetic energy.

States of Matter: a review

KMT & Changing State of Matter

• Gases- Attractions are insignificant

• Liquids- Attractions are more important, leading to a more ordered state

• Solids- Attractions are most important with a very ordered state!

KMT & Changing State

• Involves adding or removing energy (changing temperature) or changing pressure.

KMT & Changing States of Matter

• What happens, on a molecular level, when you add heat to a solid?o Molecules vibrate more rapidlyo Molecules “escape” to the liquid states and slide past each other.

• What happens when you boil/evaporate a liquid?o Molecules absorb more energy, move fastero Can break weak bonds that keep them liquid and “escape: into the gas

state.

KMT and Changing State of Matter

• The opposite occurs when you cool a gas down until it becomes a liquid and then cool the liquid until it solidifies.

What happens when we change pressure?

• Pressure – the force per unit area

• Volume- amount of space an object takes up• Temperature- average kinetic energy of the

particles• These 3 concepts are related to each other!

Pressure, Volume, & Temperature

• What would happen to the pressure from the molecules in the balloon if I decreased the volume?

Pressure & Volume• Decreasing the Volume would Increase the

Pressure

V P

• There is an inverse relationship between pressure and volume!

Volume & Temperature

• What would happen to the balloon if I increased the temperature?

Volume & Temperature

• Adding heat would increase the speed of the molecules, which increases the pressure inside the balloon, which increases the volume!