Expansion and Contraction Grade 7 Unit 3 Topic 4 Expansion and Contraction

Review: Particle Model of Matter All substances are made of tiny particles too small to be seen with the naked eye. The particles have spaces between them. The particles are always in motion – vibrating, rotating, and (in liquids and gases) moving The motion of particles increases when the temperature increases. The motion of the particles decreases when the temperature decreases.

Expansion The Particle Model of Matter tells us that as materials warm up their particles move faster and spread apart. This causes the material to expand. Expand: To increase in volume.

Contraction As materials cool down the particle model of matter says that their particles move slower and move closer together. This causes the material to contract Contract: To shrink or decrease in volume.

States of Matter There are 3 common states of matter: Solid: The material keeps both their shape and size. Solids cannot be compressed.

States of Matter There are 3 common states of matter: Liquid: The material has a definite volume (size), but no fixed shape. Liquids cannot be compressed significantly.

States of Matter There are 3 common states of matter: Gas: The material has no definite shape or volume. Gases can easily be compressed into a smaller space because there is a large amount of space between the particles.

How do particles move in a… Solid? With vibrations

How do particles move in a… Liquid? By rotating

How do particles move in a… Gas? Bouncing all over the place

Gas? By bouncing all over the place

Expansion and Contraction of Solids All solids contract and expand at different rates They have a defined form and volume They cannot be compressed into a smaller space

Expansion and Contraction of Solids Civil engineers have to think about expansion and contraction when planning roadways, sidewalks, and bridges. The expansion of solids is very small compared to liquids and gases due to the strong interactions between particles

Expansion and Contraction of Solids

Expanding Railroad Tracks

Bridge Designs

Expansion and Contraction of Liquids They have a defined volume but not a defined form They can not be compressed When the temperature of a liquid rises, the particles turn and move a lot more, causing the substance to expand.

Expansion and Contraction in Liquids Different liquids expand and contract at different rates. A common example of the expansion and contraction of liquids is the laboratory thermometer.

Expansion and Contraction in Gases Most gases are colourless, so they are difficult to observe. Because gases always take the shape and size of their container it is difficult to observe their expansion and contraction.

Expansion and Contraction in Gases If you put gases in a flexible container such as a balloon, however, you can see that they expand and contract much more than solids.

Plasma There is a fourth state of matter called: Plasma For a material to change into the plasma state requires extremely high temperatures, like those inside the sun. In plasma, individual particles that make up the material start to break apart into tinier pieces called electrons and ions.

Videos YouTube: Eureka! Expansion and Contraction (4:00) Video starts @ 0:45 YouTube: Thermal Expansion of Solids, Liquids and Gases (2:45)

The Particle Model and Changes of State. Grade 7 Unit 3 Topic 5 The Particle Model and Changes of State.

An Overview We learned that different materials expand by different amounts as they warm up. Another difference in the way materials respond when they are heated is the amount their temperature raises when a certain amount of thermal energy is added. Some materials warm and cool quickly while others warm and cool slowly.

Heat Capacity vs. Specific Heat Capacity Definition Amount of thermal energy that warms or cools the object by one degree Celsius Amount of thermal energy that warms or cools one gram of a material by one degree Celsius Describes A particular object A particular material Depends on Mass of the object and material the object is made of Material the object is made of

Heat Capacity vs. Specific Heat Capacity Material with a low specific heat capacity will have large, rapid temperature changes when heated or cooled.

Heat Capacity vs. Specific Heat Capacity Material with a high specific heat capacity will have small, slow temperature changes when heated or cooled.

Review: Matter exists in three primary states:

Changes of State A change of state requires the input of energy in one direction and a release of energy in another. Solid  Liquid  Gas (energy is used) Gas  Liquid Solid (energy is released)

Changes of State – cont. Melting (fusion): solid to a liquid. Freezing (solidification): liquid to a solid. Note: Melting point and Freezing point of a material are the same temperature. The difference is whether energy is being added (melting) or whether it is being removed (freezing).

Changes of State – cont. Evaporation: liquid to gas or vapour. Condensation: gas or vapour into a liquid. Note: Evaporation and Condensation occur at the same temperature. The difference is whether energy is being added (evaporation) or whether it is being removed (condensation).

Changes of State – cont. Sublimation: The process in which a solid changes directly into a vapour without passing through the liquid stage.

Video: Sublimation of Iodine (2:37)

Changes of State Human Changes of State (2:46)

Simulation! https://phet.colorado.edu/en/simulation/legacy/states-of-matter

What is happening to the particles during a change in state? The arrangement of the particles changes When the energy increases, the particles become less organized

What is happening to the particles during a change in state? The total energy of a substance increases or decreases (diagonal lines on a graph) The average energy of the particles does not change therefore the temperature does not change (horizontal lines on a graph)

Melting and Boiling Points Why is it important to know the melting and boiling points for different substances? To identify a substance To know when a change in state will occur

Melting and Boiling Points – cont. Do all substances have the same melting and boiling point? No!

Evaporative Cooling In a liquid, particles are moving at many different speeds. Some of the faster-moving particles at the surface are able to escape into the air. The absence of these faster-moving particles lowers the average energy of the water, and the temperature decreases.

Evaporative Cooling Summary faster-moving particles on the surface of a liquid evaporate, escaping into the air the slower-moving particles left behind have less kinetic energy this decreases the temperature of the remaining liquid

The “Plateau Problem” Why doesn’t the temperature change during a phase change (change of state)? During a phase change the average speed of particles (temperature) stays constant. What does change is the arrangement of the particles.

“The Plateau Problem” Particles become less organized as their energy increases, so substances change from solid to liquid to gas. Particles become more organized as their energy decreases, so substances change from gas to liquid to solid.

“The Plateau Problem” During a phase change energy is being used to break bonds between particles, not change their speed. This energy change is hidden from thermometers (no temperature change) so it is called “hidden heat” or “latent heat”.

Videos The Phase Changes of Water Song (3:38)