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# Phase Changes - PowerPoint PPT Presentation

Phase Changes. Physical Science Mr. Moss RHS. Phases. When 2 states are present at the same time, we describe each as a phase. Here, we see 2 phases of water: Solid Phase Liquid Phase. Phase Change Definition.

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### Phase Changes

Physical Science

Mr. Moss

RHS

• When 2 states are present at the same time, we describe each as a phase.

• Here, we see 2 phases of water:

• Solid Phase

• Liquid Phase

• A 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

• Melting

• Freezing

• Vaporization

• Condensation

• Sublimation

• Deposition

Condensation

Vaporization

Sublimation

Melting

Freezing

• NOTE:

• The temperature of the substance DOES NOT change during a phase change!!!!

• All phase changes are related to energy and temperature.

• Law of Conservation of Energy

• Neither created or destroyed.

• Transferred or Transformed

• In phase changes, energy is either absorbed or released.

• Endothermic – energy is absorbed.

• Ice melting

• Exothermic – energy is released.

• Water freezing

• 1g of ice absorbs 334 joules (J) of energy as it melts.

• This amount of energy is the Heat of Fusion for water.

• This is another term for the melting process.

• The Triple Point is where the substance exists in all 3 states.

• The Critical Point is where, under extreme high temps and pressure, the liquid and gaseous states are indistinguishable.

• Water is a molecule made up of 2 atoms of Hydrogen and 1 atom of Oxygen.

• The arrangement of molecules becomes less orderly as water melts.

• The arrangement of molecules becomes more orderly as water freezes.

• Endothermic process

• Heat energy is transformed into increased kinetic energy.

• Causes molecules to vibrate more rapidly.

• Some gain enough to overcome the attractive forces and move from the fixed locations.

• This is the melting point.

• Any energy gained after the phase change increases the average kinetic energy and the temperature rises.

• Exothermic

• Average kinetic energy (Ke) decreases causing molecules to slow down.

• At the freezing point, the attractive forces begin to draw the molecules into an orderly arrangement.

• Continues until all have been fixed.

• Any energy removed after the phase change is complete decreased the average kinetic energy of the molecules and the temperature decreases.

• Vaporization happens when a substance changes from a liquid into a gas.

• Endothermic

• Heat of vaporization

• Water gains 2258 J of energy when it vaporizes at 100° C.

• 2 vaporization processes

• Boiling

• Evaporation

• Takes place at the surface of a liquid

• Occurs at temps below the boiling point

• Process that changes a substance from a liquid to a gas at temps below the boiling point.

• In a closed container:

• Water vapor collects above the liquid

• Pressure caused by molecules colliding with container is called vapor pressure.

• Pressure increases as temp increases.

• As you apply heat energy, temperature and vapor pressure increase.

• When vapor pressure = atmospheric pressure, the water boils.

• Called the boiling point.

• Depends on Atmospheric Pressure

• Higher elevations have less atmospheric pressure

• Takes longer to cook food.

• The phase change in which a substance changes from a gas to a liquid.

• The water vapor transferred heat to the glass and condensed into a liquid.

• Sublimation is the phase change from a solid to a gas without going through the liquid phase.

• Endothermic

• Dry Ice

• Deposition is the phase change from a gas to a solid without going through the liquid phase.

• Exothermic

• Frost on windows