Chapter 3 Section 3 Notes Phase Changes

Phase Changes A phase change is a reversible physical change that occurs when a substance changes from one state of matter to another. Examples: Melting Freezing Vaporization Condensation Sublimation Deposition

Energy and Phase Change Energy is either absorbed or released during a phase change. Endothermic change means that the change is absorbing energy from its surroundings. Exothermic change means that the change is releasing energy to its surroundings.

Heat of Fusion/Heat of Vaporization The amount of energy absorbed or released during a phase change is different for different substances. Heat of Fusion is the amount of energy required to melt one gram of a substance. Heat of Vaporization is the amount of energy required to vaporize one gram of a substance.

Melting or Fusion Occurs when a substance absorbs heat energy The rigid crystal structure of the particles breaks down so that the particles are free to move around one another. Melting Point: the temperature at which a solid changes to a liquid (physical property)

Freezing Melting point and freezing point are equal! Occurs when substance loses heat energy Particles become rigid and locked into place Freezing Point: the temperature at which the substance changes from liquid to solid. (physical property) Melting point and freezing point are equal!

Vaporization Occurs when liquid absorbs heat energy Particles are free to move apart and expand. Boiling Point: The temperature that a liquid changes to a gas. (physical property)

Evaporation Vs. Vaporization Both are phase changes from liquid to gas. Vaporization takes place all throughout the liquid. Evaporation only takes place at the surface of the liquid

Condensation Occurs when the gas loses heat energy and particles contract back together. Condensing Point: the temperature at which a gas becomes a liquid due to a loss of heat energy. (physical property)

Sublimation The physical change of a solid directly to a gaseous phase without first going through the liquid phase - Ex: snow and dry ice

Deposition Occurs when a gas or vapor changes directly into a solid without first going through the liquid phase. Example: Frost on cars

Things to Remember… The arrangement of molecules in substances become less orderly as they melt and more orderly as they freeze. The temperature of a substance does not change during a phase change. The temperatures at which substances changes phases are different for different substances and the same for the same substances.