chapter 23 change of phase. phases of matter: plasma gas liquid solid
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Pressure and Temperature
According to Gay-Lussac’s Law, as the pressure of a gas decreases, there is a corresponding decrease in the temperature.
This is why the temperature of the air drops with increasing altitude.
Evaporation
• Evaporation is a change of phase from liquid to gas that takes place at the surface of a liquid.
• Temperature is related to kinetic energy and molecules in a liquid are constantly bumping into each other; some gain energy while others lose energy.
• Occasionally, some molecules gain enough energy to escape the surface of the liquid.
• They are now considered a vapor, molecules in the gaseous phase
• Evaporation is a cooling process.
• When water molecules escape the surface of liquid water, they leave behind molecules with less kinetic energy. This results in a net cooling of the liquid.
Condensation
• The opposite process to evaporation is condensation
• Condensation is the changing of a gas to a liquid
• Condensation is a warming process
• Condensation of water vapor forms clouds
Relative Humidity
• Relative Humidity is the amount of moisture in the air compared to what the air can "hold“
• Warm air can hold more water vapor than cool air
Temperature
Tornado Preparedness
• Move to an interior portion of your home or school, away from windows during a tornado
• Do not open windows to equalize pressure! This is a myth!
• Have evacuation routes planned out ahead of time
• Do not stay in your car. Your car can become a flying projectile with you in it!
Boiling
• Evaporation takes place at the surface of a liquid• A change in phase from liquid to gas can also take place beneath the surface of a liquid• The gas that forms beneath the surface causes bubbles to form• These bubbles are buoyed upward to the surface where they escape, this change in phase is called boiling
Freezing
• When energy is withdrawn from a liquid, molecular motion slows down until the forces of attraction between the molecules causes them to get closer to one another
• The molecules then vibrate about a fixed position which causes a solid to form. This change in phase from liquid to solid is called freezing
• If sugar or salt is dissolved in the water, the freezing temperature will be lowered.
• These “foreign” molecules or ions get in the way of water molecules that ordinarily would join them together in the ice crystal structure
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