Chapter 23: Change of Phase

Matter exists in 3 main phases Phase to Phase Matter exists in 3 main phases Solid Liquid Gas State of matter dependent upon temperature and pressure (involve a transfer of energy)

Evaporation Evaporation is Phase change from liquid to gas Takes place at the surface of the liquid (hot particles leave; cool ones are left behind) A cooling process How do you cool your body? How do you stay cool at Six Flags? How do you cool a hot cup of coffee? Eureka Video – Evaporation & Condensation Tennisball activity – give all tennisballs, some colored. When colored ones reach ‘surface’ – front row – they get throw to me – notice how the temperature drops and the total number of particles drops

Condensation is Condensation Phase change from gas to liquid loss of energy due to collision loss of energy due to attractive forces A warming process Why do you feel extra warm on a muggy day?

Condensation and Evaporation are constantly taking place The Going Rate Condensation and Evaporation are constantly taking place Condensation and Evaporation occur together. A hot cup of coffee cools by evaporation, the surrounding air warms

Evaporation>Condensation-cooling The Going Rate Evaporation and Condensation take place at the same time Evaporation>Condensation-cooling Evaporation<Condensation-warming Evaporation=Condensation-equilibrium

The Going Rate What can you conclude about a dish of water on a table for several days that has no change in the water level? Why do you feel chilly after emerging from a shower? Why do you not feel as chilly if you stay in the shower to dry off?

There’s Something in the Air Saturation of air must occur for condensation to be present When slow moving molecules collide, they stick together (at higher speeds, they can bounce apart) Cloud formation attributed to condensation warm air rises = expands = cools = molecules stick together = condensation upon molecules/ions Fog - a cloud that forms near the ground

It’s Time to Chill Out Freezing Freezing temperature can be altered Change from a liquid to a solid state Freezing temperature can be altered Change in pressure Adding salt or sugar

You’re Getting Warmer Boiling Changing from liquid to gas Occurs beneath the surface Cooling process - molecules having the highest KE escape

Dependent on temperature and pressure Boiling Dependent on temperature and pressure Pressure of vapor within the bubbles > pressure of surrounding liquid Temperatures below boiling point, vapor pressure is not great enough

Boiling Higher Atmospheric Pressure Increases Boiling Point molecules are required to move faster to exert increased pressure within the bubble

Lower Pressure (high altitudes), Decreases boiling point Pressure Cooker Vapor builds up inside sealed cooker Pressure on the surface is increased Raises boiling point Increased Temp. cooks the food

Boiling and Freezing can occur at the same time Regelation 2 Phases for the price of 1 Boiling and Freezing can occur at the same time Regelation Melting takes place under pressure Freezing occurs when pressure is reduced

Let’s Energize Energy is needed to go from solid to liquid to gas Energy is released when going from gas to liquid to solid

Change of Phase a d b c a

Changes of Phase Ice (A) Energy goes to K.E. + P.E. Steeper Line = easier to heat up; less goes to P.E.

Changes of Phase Melting (B) Energy goes to P.E. No temperature change 80 calories of heat must be absorbed to melt 1 gram The temperature rises once all the ice melts

Changes of Phase Liquid Water (C) Energy goes to K.E. + P.E. Each additional calorie raises the temp. by 1 degree Celsius until it reaches boiling

Changes of Phase Vaporizing (D) Energy goes to P.E. No Temp. change 540 calories of heat must be absorbed to vaporize 1 gram

Changes of Phase Check Question How much energy is released when a gram of steam at 100ºC condenses to water at 100ºC ? How much energy is released when a gram of steam at 100ºC condenses then cools to ice water at 0ºC ?

Changes of Phase Final Question How much energy is released when you cool 20 grams of 105°C steam into -10°C ice?