Phase Change Change of State

What causes a phase change? Adding or removing thermal energy can cause a substance to change its state of matter Adding thermal energy causes the particles to move faster (increase kinetic energy) and/or increase potential energy Decreasing thermal energy causes the particles to move slower (decrease kinetic energy) and/or decrease potential energy

Solid to Liquid Melting – changing from SOLID to a LIQUID Thermal energy is ADDED until the particles have enough energy to overcome the attractive forces between them At its melting point, the particles of a solid substances break free from their fixed positions, and can now slide past one another

Liquid to Solid Freezing – changing from a LIQUID to a SOLID Thermal energy is REMOVED until the particles do not have enough energy to overcome the attractive forces between them At its freezing point, the particles of a liquid substance are moving so slowly that they can no longer move freely, and remain in a fixed position

Liquid to Gas Vaporization (evaporation/boiling) – changing from a LIQUID to a GAS (Evaporation – occurs only on the surface, Boiling – occurs throughout the liquid) Thermal energy is ADDED until the particles have enough energy to overcome the attractive forces between them During vaporization, the particles of a liquid break free from those around them and can move freely

Gas to Liquid Condensation – changing from a GAS to a LIQUID Thermal energy is REMOVED until the particles slow down, move closer, and do not have enough energy to overcome the attractive forces between them. Condensation occurs when the particles in a gas slow down and move closer together.

Solid to Gas –or- Gas to Solid Sublimation – changing from a SOLID directly to a GAS Ex/ dry ice Deposition – changing from a GAS directly to a SOLID Ex/ frost

Homework Describe what happens to the motion and energy of the particles of an ice cube when it melts. Describe what happens to the motion and energy of the particles of water when it freezes.