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I. Phase Changes

I. Phase Changes. Matter and Energy Section 2.2. Phase Changes. Gas. Liquid. Solid. Amount of heat. 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.

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I. Phase Changes

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  1. I. Phase Changes Matter and Energy Section 2.2

  2. Phase Changes Gas Liquid Solid Amount of heat

  3. 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. • The molecules themselves do not change. • What changes is the arrangement of the molecules and the space between them

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

  5. Solids can become liquids, liquids can become solids • Example: Snow melting to water at 0oC

  6. 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.

  7. 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 frozenat room temperatures. (example: chocolate bars, candles, soda cans)

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

  9. Example: Water freezes to make ice cubes at 0oC

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

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

  12. Boiling 3. Boilingis 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 • Boiling occurs when a liquid reaches a certain temperature called the boiling point, 100oC for water.

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

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

  15. Deposition • 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 carbon dioxide is cooled, it forms a solid, not a liquid.

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