Changes of Phase

Phases of Matter Four Phases of Matter: Solid Liquid Gas Plasma Change of phase occurs when we pass from one phase to another, such as water (liquid) boiling to change into vapor (gas). Water Plasma Ice Steam 24-Apr-17 Physics 1 (Garcia) SJSU

STATES OF MATTER SOLIDS Particles of solids are tightly packed, vibrating about a fixed position. Solids have a definite shape and a definite volume. Heat

STATES OF MATTER LIQUID Particles of liquids are tightly packed, but are far enough apart to slide over one another. Liquids have an indefinite shape and a definite volume. Heat

STATES OF MATTER GAS Particles of gases are very far apart and move freely. Gases have an indefinite shape and an indefinite volume. Heat

Description of Phase Change PHASE CHANGES Description of Phase Change Term for Phase Change Heat Movement During Phase Change Solid to liquid Melting Heat goes into the solid as it melts. Liquid to solid Freezing Heat leaves the liquid as it freezes.

Description of Phase Change PHASE CHANGES Description of Phase Change Term for Phase Change Heat Movement During Phase Change Liquid to gas Vaporization, which includes boiling and evaporation Heat goes into the liquid as it vaporizes. Gas to liquid Condensation Heat leaves the gas as it condenses. Solid to gas Sublimation Heat goes into the solid as it sublimates.

Will everything just be a gas? But what happens if you raise the temperature to super-high levels… between 1000°C and 1,000,000,000°C ? Will everything just be a gas?

STATES OF MATTER PLASMA A plasma is an ionized gas. A plasma is a very good conductor of electricity and is affected by magnetic fields. Plasmas, like gases have an indefinite shape and an indefinite volume. Plasma is the common state of matter

STATES OF MATTER LIQUID PLASMA SOLID GAS Tightly packed, in a regular pattern Vibrate, but do not move from place to place Close together with no regular arrangement. Vibrate, move about, and slide past each other Well separated with no regular arrangement. Vibrate and move freely at high speeds Has no definite volume or shape and is composed of electrical charged particles

Some places where plasmas are found… 1. Flames

2. Lightning

3. Aurora (Northern Lights)

The Sun is an example of a star in its plasma state

Evaporation Evaporation is a change of phase from liquid to gas that takes place at the surface of a liquid. A random molecule at the surface acquires enough energy to escape the attraction force among the molecules (which holds the liquid together). GAS LIQUID

Evaporative Cooling Because only the most energetic molecules can escape the surface, evaporation removes internal energy from the liquid, that is, evaporation cools. Brr WET CLOTH HEAT WET BODY & TOWEL WET TONGUE HEAT HEAT Wet towel cools head Wetness cools person Wet tongue cools dog

Condensation Condensation is the reverse of evaporation, a change of phase from gas to liquid that takes place at the surface of a liquid. A random molecule from the gas strikes the surface and sticks instead of bouncing back into the gas. Condensation heats. GAS LIQUID

Hot and Humid A 90 degree day in a dry climate, like San Jose, is more comfortable than a 90 degree day in a humid place like New Orleans. In a dry climate you’re cooled by evaporation, in a wet climate you’re heated by condensation. Heat index is the apparent temperature a person feels for a given humidity.

Demo: Wet/Dry Bulb Thermometer Pair of thermometers; one is kept dry while the other’s bulb is wrapped in wet cloth. Difference of their temperatures gives relative humidity. Wet bulb Dry bulb Large temperature difference indicates high or low humidity? Low humidity; evaporative cooling is significant.

Fog & Clouds Warm air rises. As it rises, it expands. As it expands, it cools. As it cools, vapor molecules condense into water droplets. This forms a cloud (or fog if warm, moist air cools near the ground). As vapor expands, it cools and tiny, visible, water droplets (liquid) condense. Cool Water vapor (gas) is invisible Warm breath feels cool when it expands Warm

Boiling When the temperature of a liquid is high enough that evaporation occurs everywhere, not just the surface, then the liquid boils. The temperature required depends on the pressure; lower the pressure, the lower the boiling temperature (boiling point). Tiny bubbles grow due to evaporation at their surface

Liquid Nitrogen Liquid nitrogen boils at atmospheric pressure and room temperature. Boiling point is -320 ºF and freezes at -346 ºF. 24-Apr-17 Physics 1 (Garcia) SJSU

Demo: Slowing Air Molecules Air molecules slow down and lose kinetic energy Balloon returns to its original state Cool balloon using liquid nitrogen Balloon slowly warms up, restoring energy

Demo: Low Pressure Boiling Water boils at room temperature if the pressure is low. Cooking at high altitudes is difficult due to this effect; coffee brewed in the mountains always tastes lukewarm.

Melting Melting is the change of phase from solid to liquid. Melting is a cooling process; the solid must absorb heat to melt.

Sublimation Sublimation is change of phase from solid to gas without passing through liquid phase. Solid carbon dioxide (dry ice) sublimates at a chilly -109 °F. Put dry ice into warm water to create dense fog of tiny water droplets.

Freezing Freezing is the opposite of melting, that is, the change of phase from liquid to solid. Heat must be removed from a liquid in order to freeze it into a solid. Lava (liquid) freezes into rock (solid), heating the seawater. Seawater (liquid) boils into vapor (gas), cooling the lava.

Energy & Changes of Phase

Heats of Fusion & Vaporization 80 cal 100 cal 540 cal 720 cal Heat of Fusion Heat Capacity Heat of Vaporization Total Energy Heating a gram of water 24-Apr-17 Physics 1 (Garcia) SJSU

Demo: Geysers Geysers