Phase Changes (Changes of State)

CA State Content Standards 3e. Students know that in solids the atoms are closely locked in position and can only vibrate; in liquids the atoms and molecules are more loosely connected and can collide with and move past one another; and in gases the atoms and molecules are free to move independently, colliding frequently. 5d. Students know physical processes include freezing and boiling, in which a material changes form with no chemical reaction.

Melting Solid  Liquid As particles heat up, they gain kinetic energy and break loose and slide past one another. In most pure substances, melting occurs at a specific temperature, called the melting point. The melting point depends on how strongly its particles are attracted. Ex: Melting candle wax

Freezing Liquid  Solid When the temperature is lowered, its particles lose energy and move more slowly. The attractions as they move slowly cause them to become a solid. ICE

Freezing

Vaporization Liquid  Gas The particles become too spread out and the attractive forces are too weak to keep the particles close together.

Condensation Gas  Liquid Occurs when thermal energy is removed, particles move closer, and attractive forces hold them together.

Sublimation Solid directly to a gas (skips the liquid stage)

Deposition (desublimation) Gas to a solid without going through the liquid state An example is water vapor changing directly to ice as frost on leaves.

Adding thermal energy (heat)

Taking away thermal energy (heat)

Brainpop Matter changing states

How can matter change from one state to another? Particles are constantly moving Change in energy changes particle motion Higher temperature causes particles to move faster

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