I can describe what happens during melting and freezing I can describe what happens during melting and freezing. I can compare evaporation and condensation. I can explain what happens during sublimation. Changes of State

Energy and Changes of State Change of State- the change of a substance from one form to another. All changes are physical changes… ice, water, steam. Particles of a substance move differently depending on the state of the substance. Particles also have different amounts of energy in different states.

Melting: SolidLiquid Energy is added. Melting is the change of state from a solid to a liquid. Adding energy to a solid increases the __?__ As __?__ increases the particles move __?__ The temp. at which a substance changes from a solid to liquid is its melting point. Melting is an endothermic change because energy is gained by the substance as it changes state.

Freezing: LiquidSolid Change of state from a liquid to solid. The temperature at which a liquid changes into a solid is the freezing point. Freezing is the __?__ of melting? Thus they occur at the same time. Removing energy will cause the particles to begin to lock in place. Freezing is an exothermic change because energy is removed from the substance as it changes.

True or false Evaporation can occur at any temperature. Boiling occurs only at the surface of a liquid. Evaporation is simply a liquid changing to a gas.

Evaporation: Liquid Gas The change of a substance from a liquid to a gas. Can occur at the surface of a liquid that is below its boiling point. Boiling is the change of a liquid to a vapor or gas, throughout the liquid. The temp at which a liquid boils is its boiling point.

Condensation: GasLiquid The change of state from a gas to a liquid. Condensation and Evaporation are the reverse of each other. Condensation point of a substance is the temperature at which the gas becomes a liquid. Condensation point is the same temp. as the boiling point at a given pressure. Energy is removed during condensation, and is a exothermic change.

Sublimation: SolidGas State in which a solid changes directly into a gas. Dry ice is much colder than ice made from water. Particles move from being tightly packed to being spread far apart. Substance must gain energy, thus sublimation is an endothermic change because energy is gained by the substance as it changes state.

Change of Temp. vs Change of State When most substances lose or gain energy, either the substance changes temp, or the state changes. Temp. of a substance is related to speed of substance’s particles. Temp of a substance does not change during the change of state. Figure 7 pg 223.

Fill in the blanks with the correct word _____ is the change from liquid to gas. _____ is the change from liquid to solid. _____ is the change from solid to liquid. _____ is the change from gas to liquid.

Closure What are two changes of state that are endothermic? Do the particles of a substance move faster or slower as the substances is heated? When water evaporates, has a chemical change or a physical change?