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Section 3.3
Phase Changes
Phase Change- is the reversible physical change that occurs when a substance changes from one state of matter to another.There are 6 common phase changes:1. Melting2. Freezing3. Vaporization4. Condensation5. Sublimation6. Deposition
Phase Change Diagram
Gas
LiquidSolid
• The temperature of a substance does not change during a phase change.
• Energy is either absorbed or released during a phase change.
• Endothermic change- is where the system absorbs energy from the surroundings.
• Ex: Melting (also called fusion)- need heat• The amount of energy a substance must
absorb to change from a solid to a liquid is called the heat of fusion.
• Exothermic change- the system releases energy to its surroundings.
• Ex: Freezing- release heat to freezeMelting and Freezing• The arrangement of molecules in water
become less orderly as water melts and more orderly as water freezes.
• Substances do not have to be cold to freeze. Means becoming a solid.
• Ex: Cookies baking
Vaporization and Condensation
• Vaporization is an endothermic process.• Changing from a liquid to a gas.• Heat of vaporization is the amount of energy a
substance must absorb to change from a liquid to a gas.
• Evaporation• The process that changes a substance from a
liquid to a gas temperature below the substance’s boiling point.
• It takes place at the surface of a liquid.• Vapor pressure- the pressure caused by collisions
of this vapor and the walls of the closed container.• Boiling- (for water) this is where the vapor
pressure becomes equal to the atmospheric pressure.
• Condensation-the phase change in which a substance changes from a gas to a liquid.
• This is an exothermic process.• Water vapors transfer heat to an object and cools
into a liquid. Ex: Dew on grass
Sublimation and Deposition• Sublimation- the phase change in which a
substance changes from a solid to a gas or vapor.
• This is an endothermic process.• Ex: Dry ice (solid carbon dioxide)• Deposition- the phase change in which a
substance changes from a gas or vapor directly to a solid.
• This is an exothermic process.• Ex: Frost
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