Changes of Phase

Apr 20, 2023 Physics 1 (Garcia) SJSU

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).

Ice

Water

SteamPlasma

STATES OF MATTERSOLIDS

•Particles of solids are tightly packed, vibrating about a fixed position.

•Solids have a definite shape and a definite volume. Heat

STATES OF MATTERLIQUID

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 MATTERGAS

Particles of gases are very far apart and move freely.

Gases have an indefinite shape and an indefinite volume. Heat

PHASE CHANGESDescription of Phase Change

Term for Phase Change

Heat Movement DuringPhase Change

Solid to liquid

MeltingHeat goes into the solid as it melts.

Liquid to solid

FreezingHeat leaves the liquid as it freezes.

PHASE CHANGESDescription 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

CondensationHeat leaves the gas as it condenses.

Solid to gas SublimationHeat goes into the solid as it sublimates.

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 MATTERPLASMA

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

SOLID LIQUID GAS PLASMA

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.

GAS

LIQUID

A random molecule at the surface acquires enough energy to escape the attraction force among the molecules (which holds the liquid together).

Evaporative Cooling

Because only the most energetic molecules can escape the surface, evaporation removes internal energy from the liquid, that is, evaporation cools.

WETCLOTH

Wet towel cools head

WETTONGUE

Wet tongue cools dog

WETBODY &TOWEL

Wetness cools person

Brr

HEAT

HEATHEAT

Condensation

Condensation is the reverse of evaporation, a change of phase from gas to liquid that takes place at the surface of a liquid.

GAS

LIQUID

A random molecule from the gas strikes the surface and sticks instead of bouncing back into the gas.

Condensation heats.

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.

Large temperature difference indicates high or low humidity?Low humidity; evaporative cooling is significant.

Dry bulb

Wet bulb

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).

Warm

Cool

Warm breath feels cool when it expands

Water vapor(gas) is invisible

As vapor expands, it coolsand tiny, visible, water droplets (liquid) condense.

Tiny bubbles grow due to evaporation at their surface

BoilingWhen 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).

Apr 20, 2023 Physics 1 (Garcia) SJSU

Liquid NitrogenLiquid nitrogen boils at

atmospheric pressure and room temperature.

Boiling point is -320 ºF and freezes at -346 ºF.

Demo: Slowing Air Molecules

Cool balloon using liquid nitrogen

Air molecules slow down and lose kinetic energy

Balloon slowly warms up,

restoring energy

Balloon returns to its original state

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.

MeltingMelting 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

Apr 20, 2023 Physics 1 (Garcia) SJSU

Heats of Fusion & Vaporization

Heating a gram of water

80 cal 100 cal 540 cal 720 calHeat of Fusion

Heat Capacity Heat of Vaporization

Total Energy