Phase Changes

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 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

Deposition Condensation Vaporization Sublimation Melting Freezing

Phase Change NOTE: The temperature of the substance DOES NOT change during a phase change!!!! All phase changes are related to energy and temperature.

Energy during Phase Changes 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

Phase Diagrams

Phase Diagrams

Triple and Critical Point 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.

Melting & Freezing 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.

Melting 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.

Freezing 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 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

Evaporation 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.

Boiling 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.

Condensation 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 & Deposition 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