Phase ChangesPhase Changes Recall that matter exists in 3 states or phases: Recall that matter exists in 3 states or phases:

Solid, Liquid, and GasSolid, Liquid, and Gas A A phase changephase change occurs when there is a occurs when there is a

change in temperature of a substancechange in temperature of a substance HeatingHeating (raising temperature) causes (raising temperature) causes

particles to particles to move fastermove faster and and further apartfurther apart – Ex: melting solid chocolate into liquid when Ex: melting solid chocolate into liquid when

heated over the stoveheated over the stove Cooling Cooling (lowering temperature) causes (lowering temperature) causes

particles to particles to slow downslow down and and come closer come closer togethertogether– Ex: Evaporated water in the air cools, and Ex: Evaporated water in the air cools, and

condenses into liquid water to form cloudscondenses into liquid water to form clouds

**Particles of matter are constantly in motion. **The higher the temperature, the faster the particles will move.

Phase Change Diagram

Freezing

Melting

Condensation

Evaporation

SolidLiquidGas

Phase Changes:Phase Changes: Freezing Freezing – a change from a – a change from a liquid to a solid stateliquid to a solid state, ,

caused by a lowered temperaturecaused by a lowered temperature

MeltingMelting – a change from a – a change from a solid to a liquid statesolid to a liquid state, , caused by a raised temperaturecaused by a raised temperature

EvaporationEvaporation – a change from a – a change from a liquid to a gaseous liquid to a gaseous statestate, caused by a raised temperature, caused by a raised temperature

CondensationCondensation – a change from a – a change from a gaseous state to gaseous state to a liquid statea liquid state, caused by a lowered temperature, caused by a lowered temperature

**Sublimation**Sublimation – a change from a – a change from a solid to a gassolid to a gas without going through the liquid statewithout going through the liquid state– Ex: Ex: Dry iceDry ice evaporating is Carbon Dioxide evaporating is Carbon Dioxide

changing from a solid directly to a gas, changing from a solid directly to a gas, skipping skipping the liquid phasethe liquid phase

Phase ChangesPhase Changes When When Matter is heated:Matter is heated:

– Melting: Melting: Solid Solid LiquidLiquid

– Evaporation: Evaporation: Liquid Liquid Gas Gas

When When Matter is cooled:Matter is cooled:– Condensation: Condensation:

Gas Gas Liquid Liquid

– Freezing: Freezing: Liquid Liquid Solid Solid

Water is the exception to the Rule!Water is the exception to the Rule! Most substances, when freezing, Most substances, when freezing,

have particles that move closer have particles that move closer togethertogether

Water actually expands when Water actually expands when frozen between 0° and 4° frozen between 0° and 4° CelsiusCelsius

Water molecules form a crystalline Water molecules form a crystalline structure that makes the structure that makes the substance expand slightlysubstance expand slightly

This is why you shouldn’t freeze a This is why you shouldn’t freeze a water bottle with the lid onwater bottle with the lid on

The water will expand in the bottleThe water will expand in the bottle This is why ice floats in waterThis is why ice floats in water The The particles expandparticles expand, and are , and are

actually lighter than the liquid actually lighter than the liquid waterwater

This is how potholes in the street form

Water is constantly undergoing phase Water is constantly undergoing phase changes throughout the Water Cyclechanges throughout the Water Cycle

Accumulation

Underground Runoff

Ground water