4CHAPTER

44 Unit C: Heat in the Environment NEL

CHAPTER

77 Chapter Review

SUGGESTED ANSWERS

WHAT DO YOU REMEMBER?

1. (a) Humans wear coats to keep warm. They also build fires to warm up.

(b) Some animals such as lizards sit out in the sun on rocks to warm up. Other animals, like many birds,migrate to warmer areas in order to stay warm.

2. The particle theory says that all matter is made of particles that are moving around. Particles have spacesbetween them and are attracted to each other. Particles move faster as they absorb more energy.

3. Table 1 Descriptions of Three States of Matter

warmer air

gas

warmer air

liquid

cooler glass cooler glass

Water vapour on outsideof glass — no droplets

Liquid water onoutside of glass

4. Gas particles move so fast, bonds cannot form easily between individual particles. Fast-moving particlesmove greater distances, so when gases are heated their particles move even faster and the gas expands.

5. Heat is the transfer of thermal energy from a warmer object to a cooler object.

6. (a) Sample answer: The metal in a bridge expands in the heat. So does the wood in a desk drawer.

(b) Sample answer: Mercury in a thermometer expands when the temperature increases. As Earth’stemperature increases, the oceans expand.

(c) Sample answer: Overinflated car tires can burst when they expand. A balloon expands when the gasinside is heated.

WHAT DO YOU UNDERSTAND?

7. (a) Sample answer: I light a fire to cook food when camping. I wear heavy clothing to keep warm in thewinter. I wear light clothing to keep from overheating in the summer. I heat solder to join metal inshop class. I blow on hot liquids to keep from burning myself while drinking.

(b) Sample answer: Snow melting is an example of a change of state. So is steam forming when you takea shower. Ice cubes freezing are also an example of a change of state.

8. On a hot day, the extra thermal energy causes the particles in a solid to vibrate more quickly and expand. Ifthere were no expansion joints then the heat would cause the swelling bridge to buckle and possibly break.

9. (a) The cold water slows down the quickly moving particles of water vapour in the air outside the glass.As the particles come together, they condense into liquid form on the side of the glass.

Solid Liquid Gas

Volume constant fairly constant changing

Shape definite takes shape of container takes shape of container

Type of particle motion vibrating vibrate, rotate, move past each vibrate, rotate, move past eachother other

Spaces between particles small small, but greater than in a solid large

NEL Chapter 7 Heating and Cooling 45

(b) The solid butter melts into a liquid as the skillet gets hot because the particles in the butter start tomove away faster and farther from each other. The moving particles of a liquid take the shape of theircontainer, so the melted butter slides down the side of the skillet.

solid liquid

hot pan hot pan

°C °C

cold air

(c) As the temperature drops, the particles in the red liquid move more slowly and move closer together.This causes the liquid to contract, and the line lowers.

10. Sweating involves a change from liquid to gas—the sweat evaporates from your body.

11. The heat from the stove causes water particles in the pot to absorb energy and turn into water vapour, orgas. As the gas gets hotter it expands and pushes the lid up, letting some of the water vapour escape.

12. Sample answer: Hot air balloons work because of thermal expansion. Hot air is less dense than cool airbecause the particles in hot air are moving more quickly and covering greater distances; therefore a givenamount of hot air will contain fewer particles than an equivalent amount of cool air. Less dense air willrise. The force of the rising hot air is great enough to lift the basket with the people inside.

SOLVE A PROBLEM!

13. (a) When a metal lid is heated by the hot water, it expands faster than the glass jar. Even a slightexpansion can loosen the lid’s grip on the jar.

(b) The mechanic should heat the nut. Just like the lid on a jar, the nut will expand enough to loosen itsgrip on the bolt, making it easier to remove with a wrench and pliers.

14. (a) Wet clothing dries because the water molecules in the clothing absorb the Sun’s energy. Eventuallythose water molecules absorb enough energy to heat up and evaporate as a gas.

(b) Yes, eventually the clothes will dry, although it could take a long time. As long as it is sunny, thewater molecules will absorb the Sun’s energy and eventually turn from liquid to gas.

(c) Juicy vegetables will eventually become dried out because the water in them will be drawn to the surfaceand form ice crystals. The ice crystals will get bigger as water particles from inside the freezer attachthemselves to the vegetables. The best way to prevent this is to put the vegetables in a plastic bag, whichblocks the ice crystals from the surrounding air.

46 Unit C: Heat in the Environment NEL

15. (a) The strip bends when it is heated because one side expands more than the other side.(b) Sample answer: Bimetallic strips are used in thermostats. When the temperature drops, the strip

bends in one direction (or, if the strip has been coiled, the coil tightens); this completes a circuit,allowing hot air to flow from the furnace. As the temperature rises, the strip bends in the oppositedirection (or the coil unwinds), breaking the circuit and stopping the flow of hot air.

(c) Sample answer: If you need to heat something to a certain temperature but no further, you can use abimetallic strip that will bend at that temperature. When the strip begins to bend, you know to stopheating the object.

CREATE AND EVALUATE!

16. Because ice is lighter, or less dense, than water, it floats. The floating ice forms a protective layer over riversand lakes in the winter, keeping the water below it from freezing as well. This allows fish and other aquaticlife forms to survive until spring. If ice were heavier than water, it would sink and the entire river or lakewould freeze and be uninhabitable for part of the year.

Sample poem: In frozen winterFar beneath the ice fish swimSafe until the thaw.

17. A thermoscope is an instrument that reveals changes in temperature, but it does not display the specifictemperature. Galileo’s thermoscope, invented in 1612, consisted of a glass bulb with a long, thin neckpartially immersed in water. Changes in temperature outside the bulb caused the air inside the bulb to expandor contract. As the temperature increased, the air inside the bulb expanded, forcing water into the neck; as thetemperature decreased, the air inside the bulb contracted, letting water escape. This is similar to aconventional thermometer—as the temperature changes, the liquid inside the thermometer rises and falls.Today’s thermometers are more useful, however, because they let you measure and record the rising and fallingtemperature.

REFLECT ON YOUR LEARNING — SUGGESTED ANSWERS

18. (a) Sample answer: Matter consists of particles moving or vibrating at different speeds. When a substanceis heated, its particles absorb energy. This energy causes the particles to vibrate or move more quickly,increasing the volume of the substance. Enough heat can cause the particles in a solid to vibrate soquickly they break their bonds; the solid then melts, or changes to a liquid. Likewise, enough heat cancause the particles in a liquid to spread so far apart that the liquid evaporates, or changes to a gas.

(b) Sample answer: How do engineers change a substance’s rate of thermal expansion?19. Sample answer: Now that I know that overinflated tires can burst when they got hot, I will be careful not

to pump too much air into the tires of my bicycle. Similarly, I will be more careful not to leave mybasketball outside overnight, so it will stay as firm and bouncy as possible.

20. Sample answer: I was most interested in learning about the many different problems that thermalexpansion and contraction can cause for engineers. I would like to know more about how they solve theseproblems, especially when designing complicated things like buildings and cars.