Phase Changes

What are Some Characteristics of

Solids?• Have a fixed shape and volume in this

state.• Not easily compressible because there is

very little space between particles.• Does not flow because the particles are

held rigidly.

What are Some Characteristics of Liquids?

• Assumes shape of the container it is in because particles have

room to move or slide past one another.

• Not easily compressible for there isn’t enough free space between particles.

Solids to LiquidsExamples from Around the House

Anything can melt!• …if you get it hot enough,

that is.

• Even solid rock can melt, and when it does, it becomes lava!

• When something is completely melted, it is called “molten”, hence the phrase “molten lava”.

How hot does something need to be to melt?

• Everything has a different melting point, the temperature at which a solid becomes a liquid.

• Let’s look into this; we’ll start with something easy…

Ice!

• Do you know what temperature ice melts into water?– 32 degrees F, or 0 degrees C

• Since the human body is much warmer than ice, if you hold it, it melts!

Chocolate!

• Chocolate melts when you hold it because its melting point is just a few degrees below average human body temperature.

(Yum!)

Caramel

• If you heat sugar (and a few other things) to really high temperatures, past sugar’s melting point, when it cools back down, it will reform into caramel.

Learning Quiz

• What sorts of things can melt?

• What do you call something when it is completely melted?

• What temperature does ice melt into water at?

• Why does chocolate melt when you hold it?

Liquid to Gas

• This is when a liquid, let’s say water, is heated past its boiling point (100°C or 212°F), then that energy breaks down the bonds that hold each water molecule together. So, those water molecules escape and become gas.

http://images.usatoday.com/tech/_photos/2006/04/11/apriltwo.jpg

Gas to Liquid

• This is a change from the gas to a liquid. This happens when vapor is cooled enough to become liquid or when it is put under enough pressure. We are going to focus on vapor cooling. For example, on a hot summer day water vapor is cooled on the sides of a cold water bottle enough to condense and make the bottle “sweat”.

Courtesy of: www.weatherquestions.com/condesation.gif

Liquid to Gas & Gas to Liquid Quiz

• What is the scientific name for the change from liquid to gas?

• Why did the balloon expand?• What phase change does the example of the

bottle sweating show?• Why does the balloon become smaller in the

second experiment?• How does temperature play a role in the

evaporation and condensation phase?

Gas Expansion

Gas Expansion

Gas Expansion

Temperature and Gas Volume

• As a gas is heated the particles of that as will grow further apart

• As a gas is cooled the particles of that gas will become closer together

• This is because heat is a type of energy– As the gas is heated the energy is transferred into the

particles and they start to move around move quickly– As the particles are heated move more quickly they spread

out so that they do not bump into each other– As particles cool down they will come closer together

Temperature and the Weight of a gas

• When gas heats up it spreads out so that there are fewer particles in a given volume, and when gas cools down it shrinks up so that there are more particles in a given volume– This is called a change in density, which means which

means a change in the amount of a substance in a given space(volume)

• If something has a high density it will weigh more than something with a low density– This is because there is simply more stuff is the same

amount of space

• This is how hot air balloons work!– The hot air inside the balloon is lighter than the air

around it so it floats

Learning Quiz – Gas Expansion

• If you heat a gas does it get smaller or larger? – Why is this?

• Which will be heavier? Cold air or hot air? – What is the difference between cold air and hot air that causes one

to weigh more?

• What is the hottest a steam can get?– Why is this important?– Is this the same for all gasses?

• How cold can steam get before it turns into a liquid?