1. Changes of state Physical Science Chapter 2.3

2. Objectives Describehow energy is involved in changes of state. Describewhat happens during melting and freezing. Compareevaporation and condensation. Explainwhat happens during sublimation. Identifythe two changes that can happen when a substance loses or gains energy. Bellringer Write a description of what must be done to liquid water to change it to ice or to change it to steam. Based on your explanation, predict what must happen to cause matter to change state.

3. Energy and changes of state Change of state change of a substance from one physical form to another. Particles move differently depending on the state of the substance. Particles also have different amounts of energy when the substance is in different states.

5. Melting: Solid to Liquid Melting change of state from a solid to a liquid. Melting point The temperature at which a solid changes to a liquid Adding Energy For a solid to melt, particles must overcome their attractions to each other. At the melting point, any energy added is used to overcome attractions between particles.

6. Freezing: Liquid to Solid Freezing Change of state from a liquid to a solid. Freezing point Temperature at which a liquid changes to a solid. Removing Energy When a liquid is at its freezing point, removing energy will cause the particles to begin locking into place.

7. Evaporation: Liquid to Gas Evaporation Change of state from a liquid to a gas. Evaporation can occur at the surface of a liquid that is below its boiling point. Boiling Change of a liquid to a gas throughout the liquid. boiling point Temperature at which a liquid boils.

9. Effects of Pressure on Boiling Point The boiling point of a liquid decreases as atmospheric pressure decreases. Atmospheric pressure is caused by the weight of the gases in the atmosphere. Atmospheric pressure is lower at higher elevations. So, the boiling point is lower on top of mountains than it is at sea level.

10. Condensation: Gas to Liquid Condensation change of state from a gas to a liquid. Condensation point the temperature at which the gas becomes a liquid. Removing Energy slows the movement of gas particles which allows them to clump together.

11. Sublimation: Solid to Gas Sublimation Change of state in which a solid changes directly into a gas. Must Gain Energy For sublimation to occur, the attractions between the particles must be completely overcome.

12. Change of Temperature vs. Change of State When most substances lose or gain energy 2 Possibilities: temperature change state change Temperature of a substance does not change until a change of state is complete.