I. Phase Changes Matter and Energy Section 2.2

Phase Changes Gas Solid Liquid Amount of heat

When matter changes from one state to another, the substance itself does not change. When matter changes from one state to another, the substance itself does not change. Water, ice, and steam (water vapor) are all the same basic substances. Water, ice, and steam (water vapor) are all the same basic substances. The molecules themselves do not change. The molecules themselves do not change. What changes is the What changes is the arrangement of the arrangement of the molecules and the molecules and the space between them space between them

Solids can become liquids, liquids can become solids A.Melting - the process by which a solid becomes a liquid 1.Different solids melt at different temperatures. 2.Melting point - The lowest temperature at which a substance at which a substance begins to melt. begins to melt.

Solids can become liquids, liquids can become solids 3.Example: Snow melting to water at 0 o C

REMEMBER: particles are always in motion, even in solids. Because the particles in a solid are bound together, they do not move from place to place- they vibrate. REMEMBER: particles are always in motion, even in solids. Because the particles in a solid are bound together, they do not move from place to place- they vibrate. As a solid heats up, the particles vibrate faster until they break loose and slide past each other-in other words turn into a liquid. As a solid heats up, the particles vibrate faster until they break loose and slide past each other-in other words turn into a liquid.

B.Freezing - the process by which a liquid becomes a solid. A frozen substance does not have to have an extremely cold temperature, some substances are frozen at room temperatures. A frozen substance does not have to have an extremely cold temperature, some substances are frozen at room temperatures. (example: chocolate bars, candles, soda cans)

1.Freezing point - the temperature at which a specific liquid becomes a solid. 2.The freezing point of a substance is the same as the melting point. At temperatures below this point the substance is a solid, At temperatures below this point the substance is a solid, above this point the above this point the substance is a liquid. substance is a liquid.

3. Example: Water freezes to make ice cubes at 0 o C

C.Vaporization – change of matter from a liquid state to a gas. 1.Vaporization occurs at the boiling point or during evaporation.

2.Evaporation - the process by which a liquid becomes a gas It occurs at the surface of a liquid It occurs at the surface of a liquid The fastest moving The fastest moving particles at the surface can break away from the liquid and escape to become gas particles.

Boiling 3. Boiling is another process by which a liquid becomes a gas. Unlike evaporation, boiling produces bubbles that contain energetic molecules that have escaped from the liquid to form a gas Unlike evaporation, boiling produces bubbles that contain energetic molecules that have escaped from the liquid to form a gas Boiling occurs when a liquid Boiling occurs when a liquid reaches a certain temperature reaches a certain temperature called the boiling point, 100 o C for called the boiling point, 100 o C for water. water.

When you cool When you cool a gas it loses energy. As the particles move more slowly, the attractions among them cause droplets to form. D. Condensation - the process by which a gas becomes a liquid.

Sublimation Under certain conditions, solids can lose particles through a process similar to evaporation. Under certain conditions, solids can lose particles through a process similar to evaporation. E.Sublimation – when solids change directly to a gas. Example: Dry ice (solid carbon dioxide) sublimates in normal atmospheric conditions. atmospheric conditions.

Deposition F.Deposition - When a gas changes directly to a solid. When you cool a gas it loses energy. As the particles move more slowly, the attractions among some them cause a solid to form. When you cool a gas it loses energy. As the particles move more slowly, the attractions among some them cause a solid to form. When carbon dioxide is cooled, it forms a solid, not a liquid. When carbon dioxide is cooled, it forms a solid, not a liquid.