Phase Changes of Matter Notes

4 Phases of matter exist solid, liquid, gas, plasma (we don’t study) Heat energy causes the physical properties to change into each of these phases

Properties of Phases Solid: has a defined volume and shape Molecules have energy to vibrate, but not freely When heated they expand; cooled they compress

Properties of Phases Liquid: Defined volume, but not a defined shape Molecules flow and move, but stay close together Heated they evaporate; cooled they condense

Properties of Phases Gases: Undefined volume and undefined shape Molecules have energy to move fast and freely; they move away from each other Heated they expand, cooled they compress

Properties of Phases Plasma: Rare on Earth Extremely high energy & dangerous Ex: the sun, lightning, fire

Properties of Phases Exothermic Change: heat energy is released into the surroundings Ex: water freezing…the water is not absorbing the cold…it is losing its heat.

Heat Energy & Phase Changes Endothermic Change: absorbs heat energy from surroundings Ex: Ice melting…ice is absorbing heat from air around it and rising above the freezing point. As the ice absorbs heat, the molecules of water move faster and start to flow away from each other

E D 100 gas C liquid B A solid Heat (thermal energy) Temperature º C. As water changes from solid to liquid to gas, what is happening to the energy of the molecules? (increasing) (click) What is happening to the temperature? (increasing) A solid Heat (thermal energy)

6 Phase Changes Melting: Solid Liquid Vaporization: Liquid Gas Occurs at melting point Vaporization: Liquid Gas Occurs at boiling point Sublimation: Solid Gas Does NOT change to Liquid phase in between Ex: dry ice

6 Phase Changes Condensation: Gas Liquid Freezing: Liquid Solid Occurs when cooling to below boiling point Freezing: Liquid Solid Occurs at freezing point Deposition: Gas Solid Does NOT change to a Liquid in between Ex: frost on car

Thermal Expansion Tendency to change shape, area and volume through transfer of heat Simply put: matter expands or contracts in size based on heat energy levels

Thermal Expansion Add heat = matter expands Remove heat = matter contracts Unique Quality of Water: Water expands when it freezes.

Why does water expand when frozen? Have you ever noticed ice cubes get larger than the liquid water they started as? If you put a bottle of water in the freezer, it will expand and possibly rupture.

Try this at home: Remove cap from a water bottle; Stand the bottle in a larger plastic dish(to catch the overflow); Carefully put in freezer overnight The ice should expand out from the mouth of the bottle. WHY???

Why water expands when frozen. As it freezes, it forms crystals, creating more space between molecules.