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CHAPTER 13

ANSWER KEY

convection current is set up with the surrounding air. This current carries heat away from the water long before the water can boil.

BLM 13-1, Why Is the Sky Blue?/ Science Inquiry Goal: Students use this sheet to help them answer questions about the colour of the sky. Answers:

(c) The final temperature of the water depends on how well the surrounding air can carry away the heat, and how much energy is coming into the jar of water. The final temperature also depends on how well the jar can absorb heat, which may depend on whether the jar is white, black, or a colour between these extremes.

1. The sky is blue. 2. It looks like a rainbow (red, orange, yellow, green, blue, and purple) as you look away from the horizon. It becomes darker as you look overhead. 3. The clouds are at different heights. The light scatters less at higher altitudes, so higher clouds are lighter. 4. Answers will vary, but the patterns noted for questions 2 and 3 should be visible.

BLM 13-3, Earth’s Energy Budget Quiz/Assessment Goal: Students assess their knowledge of Earth’s energy budget. Answers: 1.

BLM 13-2, Absorption or Reflection/Science Inquiry Goal: Students use this sheet to help them complete Science Inquiry Activity: Absorption or Reflection. Answers: 1. Answers will vary according to the results of students’ experiments. 2. the black can

Mechanism of heat transfer

(b) Most students will say yes. Some may say that the water will be about this hot, but they may have trouble expressing why they are a bit hesitant. The next question explores this in greater detail. 5. (a) Number of hours needed for water to boil at this rate =

100˚C ⫺ Starting temperature Value for the increase in temperature per hour

(b) The black paper emits radiation in all directions. When the water is cooler than the air, more thermal energy flows from the air to the water than from the water to the air. When the water is warmer than the air, the water loses thermal energy to the surrounding air. Also, a

Example

radiation

Molecules emit electromagnetic waves.

outer space

convection

Molecules move.

soup boiling in a pot

conduction

Molecular collisions transfer energy.

frying pan

3. This depends on the experiment, but the calculation is explicitly stated in the question. 4. (a) The rate of temperature increase varies between 3°C and 12°C depending on the time of year, angle of sun, and whether the can is left outside or beside a window.

Description

2. (a) It falls mainly in the infrared, visible light, and ultraviolet parts. (b) You feel the heat from the Sun (infrared), you see the Sun (visible light), and you get a sunburn (ultraviolet) unless you protect yourself. 3. One square metre held perpendicular to the Sun’s rays absorbs 1367 W of power, or 1367 J of energy, each second. 4. Black asphalt would feel hotter. Because it is black, it absorbs more energy than the white sand, which would reflect the energy. 5. Earth’s atmosphere traps heat and slows the cooling of Earth. (More technically, Earth’s atmosphere re-radiates some of the heat back to Earth instead of letting it all escape into space.) The Moon has no atmosphere to moderate the presence and absence of sunlight.

Copyright © McGraw-Hill Ryerson Limited.

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BLM 13-4, Change in Temperature of Water/Reinforcement Goal: Students reinforce their understanding of temperature changes. Answers:

Step 3: Q = mct = (50 g)(4.18 J/g•˚C)(100˚C) = 20 900 J Step 4: Q = mH˚vap = (50 g)(2260 J/g)

1. 2 102 J (200.64 J)

= 113 000 J

2. 5 103 J (5016 J)

Step 5: Q = mct

3. 1.3 104 J (13 376 J)

= (50 g)(4.18 J/g•˚C)(100˚C)

4. The temperature of the water rises 19˚C. 5. The water cools 65˚C.

= 20 900 J Step 6: Step 1: 8360 J Step 2: 16 650 J

BLM 13-5, Changes of State of Water/Skill Builder Goal: Students practise using the triangle formula to solve problems related to the changes of state of water. Answers:

Step 3: 20 900 J Step 4: 113 000 J Step 5: 20 900 J Total energy = 8360 J 16 650 J 20 900 J 113 000 J 20 900 J = 179 810 J

1. 680 kJ

Therefore 1.8 105 J of energy are needed to warm ice at –40˚C to steam at 200˚C.

2. 170 kJ 3. 6.66 104 J 4. 5.3 105 J

2. 43 890 J is removed to warm the ice to 0˚C, 99 900 J to melt the ice, and 22 572 J to warm it to 18˚C. The total is 166 362 J (1.66 105 J using significant figures).

5. 8.0 g (7.965 g before rounding) 6. 25 g 7. (a) 855 J/g.

3. The steam gives off 2.299 109 J as it cools to the boiling point, then 5.65 109 J is released as the steam condenses, and finally 7.315 108 J as the water cools to 30˚C. The total is 8.68 109 J.

(b) ethanol

BLM 13-6, Change in Temperature Through Changes of State/Skill Builder Goal: Students further their understanding of the processes involved in changes of state. Answers: 1. The steps are laid out, in progressively less detail, to allow students to fill in the data. Step 2: Q = mH˚fus = (50 g)(333 J/g) = 16 650 J

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4. 25 080 J are needed to bring the water to 100˚C, 169 500 J to turn the water into steam, and 15 675 J to heat the steam to 150˚C. The total is 2.10 105 J. 5. Melting the ice takes 6660 J of energy, raising the water temperature to 100˚C takes 8360 J, and evaporating the water takes 45 200 J. The total is 6.02 104 J. 6. The steam loses 1.254 106 J while cooling to 100˚C, 1.356 106 J while condensing, 2.508 105 J while cooling to 0˚C, 1.998 105 J while freezing, and 1.0032 105 J while cooling to 40˚C. The total is 3.16 106 J.


CHAPTER 13

ANSWER KEY

you would breathe in nearly as much water as you would breathe out. In a desert, the air is very dry. Since you would breathe out more water than you would breathe in, dehydration is always a danger.

BLM 13-7, Moisture in the Air/ Reinforcement Goal: Students further their understanding of moisture in the air. Answers:

5. House air comes from the outside, and so does all the moisture in the air. In the summer, parts of a house may be cooler than the surrounding air. If outside air is saturated, some of the water condenses onto something once it is inside the house. In the winter, even saturated air is very dry at the temperatures found inside a house. Therefore water has to be added.

1. The air in a desert is very hot during the day, so it can hold a lot of moisture. At night, the air cools quickly and the moisture condenses out of the air. The moisture condenses as dew because the sand cools very quickly compared with the air. 2. Most of the water in Nunavut is left over from the last ice age, since Nunavut does not get hot enough to evaporate much water. Cold air cannot carry much water out of the lakes.

BLM 13-8, The Water Cycle/ Overhead Master

3. Cold air can hold less moisture, so winter air is drier than summer air. Moist air cools off more slowly than dry air because of the large specific heat capacity of water. Thus the drier air of winter cools faster, making the temperature drop even more than in the summer. 4. A rain forest has many plants to evaporate moisture (transpiration) into the air. This makes the air saturated, or nearly saturated. Therefore

Answers: not applicable

BLM 13-9, Review of Energy and Water/Assessment Goal: Students assess their knowledge of energy and water. Answers: 1.

Process

Associated property

cooling

specific heat of water

condensation

latent heat of vaporization

cooling


freezing cooling

Change in temperature

Energy released

20˚C

8 360 J

0˚C

226 000 J

100˚C

41 800 J

latent heat of fusion

0˚C

33 300 J


30˚C

12 540 J

2. Warm air can absorb more water from the clothes. 3. (a) 3.84 g (b) 0.78 g 4. Air feels colder because it must be warmed by a person’s body. Saturated air has water, and the large specific heat capacity of water means that more energy is needed to warm it up.


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4. 7.87 ⫻ 10–2˚C

BLM 13-10, Does Solar Energy Heat the Air?/Reinforcement

5. 2.07 ⫻ 106 J

Goal: Students review their understanding of the relationship between solar energy and warming of the air, after completing Science Inquiry Activity: Does Solar Energy Heat the Air? Answers:

6. 16.2˚C 7. No. The air is warmed by less than 0.1˚C per hour, but the soil can warm up to 16.2˚C in the same time. So the soil rapidly becomes warmer than the air, and when this happens it starts to warm the air.

1. 4.9 ⫻ 10 6 kJ/h 2. Sunlight has to pass through the atmosphere to reach a rooftop solar cell, and the atmosphere absorbs some of the energy. The cell would have to be kept clean. (Trivia: Israeli citizens with rooftop solar generators report 3 percent more back injuries, chiefly from falling from the roof while cleaning their solar cells!) The Sun does not shine all the time. 3. 7.87 ⫻ 105 J

Level of atmosphere

BLM 13-11, Sea Breezes and Land Breezes/Overhead Master Answers: not applicable

BLM 13-12, Levels of the Atmosphere/Reinforcement Goal: Students review the levels of the atmosphere. Answers:

Height of bottom

Height of top

Temperature of bottom

Temperature of top

What you can find there

ground temperature

⫺57˚C

clouds, birds

22–25 km

⫺57˚C

⫺57˚C

tops of thunderstorms, ozone layer

22–25 km

55 km

⫺57˚C

⫺2˚C

ozone layer

mesopause

55 km

60 km

⫺2˚C

⫺2˚C

large meteors

mesosphere

60 km

85 km

⫺2˚C

⫺95˚C

meteors burning up

thermopause

85 km

100 km

⫺95˚C

⫺95˚C

ions

100 km

indefinite (probably about 400 km)

⫺95˚C

about 135˚C

troposphere

0 km

8–11 km

stratopause

9 km

stratosphere

thermosphere

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ions, aurora, satellites

CHAPTER 13

ANSWER KEY

BLM 13-13, Atmospheric Composition/Reinforcement Goal: Students review their knowledge of the composition of Earth’s atmosphere and greenhouse gases. Answers: 1. Gas nitrogen oxygen argon carbon dioxide everything else

Percent 78 21 0.93 0.03 0.04

2. Answers will vary. Statistically, about 90 percent of students will choose the figure from the textbook. 3. The amount of water vapour varies much more with time and place than do the amounts of other gases. 4. The only greenhouse gas in the table is carbon dioxide. Other greenhouse gases are methane, ozone, and CFCs (ChloroFloroCarbons). 5. This approximation is rather good, being accurate to within 4 percent. 6. Without greenhouse gases to moderate the climate, there would be temperature swings such as those found on the Moon: days near 115˚C, nights near ⫺80˚C. The average temperature on Earth would be below 0˚C! 7. As well as the reasons given in Unit 1, rising levels of greenhouse gases may lead to more severe weather (heat in summer, cold in winter), warmer temperatures year-round, drier weather in some regions (especially the interior of continents), wetter weather in some regions (especially coastal regions), more storms (such as tornadoes, hurricanes, and thunderstorms), and the melting of polar ice caps.

Answers: 1

P

2

3

R E S S E T 9 L R A A A T T I O V S E P H H U E M R I E D 17 I O N O T Y 19 C A R

U 10

D E W P O I N T

S

B

R

Goal: Students check their understanding of terms related to the atmosphere.

5

6

7

8

C O N D U C T I O N O I L R X 13 I A T I O N T T O Y C U N V R R P G O 14 R S E O A O C E A N O U C G V S N D R L T E I P E 15 A A I N O H S U N T O L E A S 16 I N I C E R T A N T E U T O F R I N R A O P H E R E A T N R E 18 E C L O U D O N D I O X I D E 12

S

BLM 13-15, Heating Land and Air Quiz /Assessment Goal: Students assess their knowledge of the interactions of solar energy with land and air. Answers: 1. Water has a larger specific heat capacity. Water moves (convection). Water is clear, so radiant energy penetrates water to a greater depth than soil. 2. The ground emits infrared radiation, which is absorbed by greenhouse gases in the atmosphere. As the lowest layer of air warms, it becomes less dense and rises, bringing warm air into the atmosphere (convection). Energetic molecules in the ground transfer their energy to nearby air molecules by colliding with them (conduction). 3.

D

C B

E A

land

BLM 13-14, The Atmosphere/ Vocabulary Check

4

E

11

sea

4. the ionosphere 5. 100 kg


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BLM 13-16, Chapter 13 Review/ Reinforcement

16. Atmospheric pressure is the weight per area of the atmosphere (measured in pascals, which are newtons per square metre).

Goal: Students assess their understanding of the relationships between solar energy and the factors that have an impact on weather. Answers:

17. The solar constant is the amount of energy that hits a 1 m2 column of air per second. The column is perpendicular to the Sun’s rays.

1. T

18. 16 650 J (or 1.7 ⫻ 104 J) of energy is required. 19. (a) No. The air is not saturated.

2. T

(b) The relative humidity is 75 percent.

3. F

20. Answers may vary slightly. Students should include a sketch similar to the one on page 441 of the student textbook (or in question 3 of BLM 13-15). Students should mention that the land warms faster than the water. Therefore the air over the land will warm faster, too. This air rises, drawing in cooler air from over the water. The air high over the water falls to take the place of the air moving to the land, which draws the air that rose from the land out to sea to take its place. After the first steps (the land warms faster, causing air to rise), the order is not important.

4. T 5. F 6. T 7. F 8. wind 9. faster 10. stratosphere 11. nitrogen, oxygen 12. Convection is warm air moving to cooler areas. 13. The specific heat capacity of a substance is the amount of heat required to raise the temperature of 1 g of this substance by 1˚C. 14. Relative humidity is a measure of the amount of moisture in the air, compared with the maximum amount that could be there.

21. The high specific heat capacity of water means that more energy is needed to raise its temperature than to raise the temperature of the surrounding mug. 22. Earth absorbs radiant energy (infrared, visible, and ultraviolet light) from the Sun. Earth constantly re-radiates energy, in the form of infrared radiation, back into space.

15. The troposphere is the lower 10 km of the atmosphere, where weather occurs.

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