Kinetic Theory of Matter: Solids, Liquids, Gases

Kinetic Theory of Matter

• Solids have a fixed shape and volume, and high density
• Atoms vibrate, but cannot change location
• Particles are closely packed in a fixed, regular pattern

Kinetic Theory of Liquids

• Liquids have a fixed volume but take the shape of their container
• Liquids are generally less dense than solids, but more dense than gases
• Particles move and slide past each other, allowing them to flow

Kinetic Theory of Gases

• Gases have no fixed volume and take the shape of their container
• Gases have a very low density
• Particles are far apart, and move randomly at high speed (around 500 m/s) in all directions
• Particles collide with each other and container walls, creating pressure

Summary of Solid, Liquid, and Gas Properties

States of Matter and State Changes

• Melting: Solid to liquid; requires heat energy; occurs at a specific temperature (melting point)

• Boiling: Liquid to gas; requires heat energy; occurs at a specific temperature (boiling point)

• Freezing: Liquid to solid; reverse of melting; occurs at the same temperature (melting point)

• Evaporation: Liquid to gas; occurs at the surface of liquids over a temperature range; below the boiling point.

• Condensation: Gas to liquid; cooling a gas causes particles to lose energy and group together, forming a liquid; occurs over a temperature range.

• Sublimation: Solid to gas; few solids undergo this; like iodine or solid carbon dioxide. The reverse reaction is desublimation / deposition.

Pressure and Temperature in Gases

• Changes in temperature and pressure affect the volume of gases
• As gas temperature increases, the gas volume increases; the density decreases
• If a gas's container is compressed (volume is decreased), its pressure increases
• Gas particles are in constant, random motion
• Pressure is created by particles colliding with the inside walls of a container.

Heating and Cooling Curves

• As substances are heated, kinetic energy increases, causing particles to vibrate more rapidly
• Changes in state are shown by horizontal sections in a heating curve, where temperature remains constant
• Cooling curves are the mirror image of heating curves, showing temperature decrease corresponding to phase changes.