Chapter 2 Energy and Matter 2.1 Energy

Transcription

1 Chapter 2 Energy and Matter 2.1 Energy 1

2 Energy Energy makes objects move. makes things stop. is needed to do work. 2

3 Work Work is done when you climb. you lift a bag of groceries. you ride a bicycle. you breathe. your heart pumps blood. water goes over a dam. Copyright 2009 by Pearson Education, Inc. 3

4 Potential Energy Potential energy is stored energy. Examples are water behind a dam. a compressed spring. chemical bonds in gasoline, coal, or food. Copyright 2009 by Pearson Education, Inc. 4

5 Kinetic Energy Kinetic energy is the energy of motion. Examples are swimming. water flowing over a dam. working out. burning gasoline. Copyright 2009 by Pearson Education, Inc. 5

6 Learning Check Identify the energy as potential or kinetic. A. Rollerblading B. a peanut butter and jelly sandwich C. mowing the lawn D. gasoline in the gas tank 6

7 Solution Identify the energy as potential or kinetic. A. Rollerblading (kinetic) B. a peanut butter and jelly sandwich (potential) C. mowing the lawn (kinetic) D. gasoline in the gas tank (potential) 7

8 Units for Measuring Energy or Heat Heat is measured in joules or calories Joules (J) = 1 calorie (cal) 1 kj = 1000 J 1 kilocalorie (kcal) = 1000 calories (cal) 8

9 Examples of Energy In Joules 9

10 Learning Check How many cal are obtained from a pat of butter if it provides 150 J of energy when metabolized? 1) 0.36 cal 2) 36 cal 3) 630 cal 10

11 Solution How many cal are obtained from a pat of butter if it provides 150 J of energy when metabolized? Answer 2) Solution: Given: Need: Plan: Equality: Setup: 150 J calories J -> cal 1 cal = J 150 J x 1 cal = 36 cal J 11

12 Chapter 2 Energy and Matter 2.2 Energy and Nutrition Copyright 2009 by Pearson Education, Inc. 12

13 Calorimeters A calorimeter is used to measure heat transfer. can be made with a coffee cup and a thermometer. indicates the heat lost by a sample indicates the heat Copyright 2009 by Pearson Education, Inc. 13

14 Energy and Nutrition On food labels, energy is shown as the nutritional Calorie, written with a capital C. In countries other than the U.S., energy is shown in kilojoules (kj). 1 Cal = 1000 calories 1 Cal = 1 kcal 1 Cal = 1000 cal 14

15 Caloric Food Values The caloric or energy values for foods indicate the number of kcal (Cal) provided by 1 g of each type of food. Carbohydrate: Fat (lipid): Protein: 4 kcal 1 g 9 kcal 1 g 4 kcal 1 g 15

16 Energy Values for Some Foods 16

17 Energy Requirements The amount of energy needed each day depends on age, sex, and physical activity. 17

18 Learning Check A cup of whole milk contains 12 g of carbohydrate, 9 g of fat, and 5 g of protein. How many kcal (Cal) does a cup of milk contain (round answer to the tens place)? 1) 50 kcal (or Cal) 2) 80 kcal (or Cal) 3) 150 kcal (or Cal) 18

19 Solution A cup of whole milk contains 12 g of carbohydrate, 9 g of fat, and 5 g of protein. How many kcal (Cal) does a cup of milk contain? 3) 150 kcal (or Cal) 12 g carbohydrates x 4 kcal/g = 50 kcal 9 g fat x 9 kcal/g = 80 kcal 5 g protein x 4 kcal/g = 20 kcal 150 kcal 19

20 Chapter 2 Energy and Matter 2.3 Temperature Conversions Copyright 2009 by Pearson Education, Inc. 20

21 Temperature Temperature is a measure of how hot or cold an object is compared to another object. indicates that heat flows from the object with a higher temperature to the object with a lower temperature. is measured using a thermometer. Copyright 2009 by Pearson Education, Inc. 21

22 Temperature Scales Temperature Scales are Fahrenheit, Celsius, and Kelvin. have reference points for the boiling and freezing points of water. Copyright 2009 by Pearson Education, Inc. 22

23 Learning Check A. What is the temperature of freezing water? 1) 0 F 2) 0 C 3) 0 K B. What is the temperature of boiling water? 1) 100 F 2) 32 F 3) 373 K C. How many Celsius units are between the boiling and freezing points of water? 1) 100 2) 180 3)

24 Solution A. What is the temperature of freezing water? 2) 0 C B. What is the temperature of boiling water? 3) 373 K C. How many Celsius units are between the boiling and freezing points of water? 1)

25 Fahrenheit Formula On the Fahrenheit scale, there are 180 F between the freezing and boiling points; on the Celsius scale there are 100 C. 180 F = 9 F = 1.8 F 100 C 5 C 1 C In the formula for the Fahrenheit temperature, adding 32 adjusts the zero point of water from 0 C to 32 F. T F = 9/5 T C + 32 or T F = 1.8 T C

26 Celsius Formula T C is obtained by rearranging the equation for T F. T F = 1.8T C + 32 Subtract 32 from both sides. T F - 32 = 1.8 T C ( ) T F - 32 = 1.8 T C Divide by 1.8 = F - 32 = 1.8 T C T F -32 = T C

27 Solving A Temperature Problem A person with hypothermia has a body temperature of 34.8 C. What is that temperature in F? T F = 1.8 T C + 32 T F = 1.8 (34.8 C) + 32 exact 3 SFs exact = (addition) = 94.6 F tenth s Copyright 2009 by Pearson Education, Inc. 27

28 Learning Check The normal body temperature of a chickadee is F. What is that temperature on the Celsius scale? 1) 73.8 C 2) 58.8 C 3) 41.0 C 28

29 Solution 3) 41.0 C T C = (T F 32 ) 1.8 = ( exact) 1.8 = 73.8 F (3 SFs) = 41.0 C 1.8 (exact) (division, 3SFs) 29

30 Learning Check A pepperoni pizza is baked at 455 F. What temperature is needed on the Celsius scale? 1) 423 C 2) 235 C 3) 221 C 30

31 Solution A pepperoni pizza is baked at 455 F. What temperature is needed on the Celsius scale? 2) 235 C T F -32 = T C 1.8 ( ) = 235 C

32 Learning Check On a cold winter day, the temperature is 15 C. What is that temperature in F? 1) 19 F 2) 59 F 3) 5 F 32

33 Solution Answer 3) 5 F Solution: T F = 1.8T C + 32 T F = 1.8 ( 15 C) + 32 = 27 F + 32 = 5 F Note: Be sure to use the change sign key on your calculator to enter the minus ( ) sign. 1.8 x 15 +/ = 27 33

34 Study Tip: Temperature Math The temperature equation involves the exact numbers 1.8 and 32. Only the temperature is measured. To convert C to F, a multiplication rule is followed by an addition rule. multiplication step 1.8 ( 15 C) = 27 F (2 SF) addition step 27 F (ones place) + 32 (exact) = 5 F (ones place) 34

35 Kelvin Temperature Scale The Kelvin temperature scale has 100 units between the freezing and boiling points of water. 100 K = 100 C or 1 K = 1 C is obtained by adding 273 to the Celsius temperature. T K = T C contains the lowest possible temperature, absolute zero (0 K). 0 K = 273 C 35

36 Temperatures 36

37 Learning Check What is normal body temperature of 37 C in kelvins? 1) 236 K 2) 310 K 3) 342 K 37

38 Solution What is normal body temperature of 37 C in kelvins? 2) 310 K T K = T C = 37 C = 310. K (to ones place) 38

39 Chapter 2 Energy and Matter 2.4 Specific Heat Copyright 2009 by Pearson Education, Inc. 39

40 Specific Heat Specific heat is different for different substances. is the amount of heat that raises the temperature of 1 g of a substance by 1 C. in the SI system has units of J/g C. in the metric system has units of cal/g C. 40

41 Examples of Specific Heats 41

42 Learning Check A. When ocean water cools, the surrounding air 1) cools. 2) warms. 3) stays the same. B. Sand in the desert is hot in the day, and cool at night. Sand must have a 1) high specific heat. 2) low specific heat. 42

43 Solution A. When ocean water cools, the surrounding air 2) warms. B. Sand in the desert is hot in the day, and cool at night. Sand must have a 2) low specific heat. 43

44 Learning Check What is the specific heat if 24.8 g of a metal absorbs 275 J of energy and the temperature rises from 20.2 C to 24.5 C? 44

45 Solution Given: 24.8 g metal, 275 J of energy, 20.2 C to 24.5 C Need: Specific heat J/g C Plan: specific heat (SH) = Heat (J) g C T = 24.5 C 20.2 C = 4.3 C Setup: 275 J = 2.6 J/g C (24.8 g)(4.3 C) 45

46 Heat Equation The amount of heat lost or gained by a substance is calculated from the mass of substance (g). temperature change ( T). specific heat of the substance (J/g C). This is expressed as the heat equation. Heat = g x C x J = J g C 46

47 Learning Check How many kj are needed to raise the temperature of 325 g of water from 15.0 C to 77.0 C? 1) 20.4 kj 2) 77.7 kj 3) 84.3 kj 47

48 Study Tip: Using Specific Heat 48

49 Solution Answer: 3) 84.3 kj 77.0 C 15.0 C = 62.0 C 325 g x 62.0 C x J x 1 kj g C 1000 J = 84.3 kj 49

50 Coral Bleaching Coral contains algae that produce sugars (food) and the bright red and orange pigments of coral. expels the algae when water temperatures increase as little as 1 C. bleaches as it loses its food supply and color. dies if the stress of higher temperatures continues. reefs in Australia and the Indian Ocean have been badly damaged by increases in ocean temperatures. 50

51 Learning Check How many kcal are absorbed by ocean water if 3 x L of water in the Caribbean has an increase of 1 C. Assume the specific heat of ocean water is the same as water. Assume the density of ocean water is 1.0 g/ml. 1) 3 x kcal 2) 3 x kcal 3) 3 x kcal 51

52 Solution ml 3 10 L 1 L 21 = 3 10 g of sea seawater water seawater 1 g 1 ml g 1 C 1 cal 1 kcal g C 1000 cal 18 = 3 10 kcal of heat absorbed (Answer 2) 52

53 Chapter 2 Energy and Matter 2.5 States of Matter Copyright 2009 by Pearson Education, Inc. 53

54 Solids Solids have a definite shape. a definite volume. particles that are close together in a fixed arrangement. particles that move very slowly. 54

55 Liquids Liquids have an indefinite shape, but a definite volume. the same shape as their container. particles that are close together, but mobile. particles that move slowly. 55

56 Gases Gases have an indefinite shape. an indefinite volume. the same shape and volume as their container. particles that are far apart. particles that move very fast. 56

57 Three States of Matter for Water Copyright 2009 by Pearson Education, Inc. 57

58 Summary of the States of Matter 58

59 Learning Check Identify each as: 1) solid, 2) liquid, or 3) gas. A. It has a definite volume, but takes the shape of the container. B. Its particles are moving rapidly. C. It fills the volume of a container. D. It has particles in a fixed arrangement. E. It has particles close together that are mobile. 59

60 Solution Identify each as: 1) solid, 2) liquid, or 3) gas. 2 A. It has a definite volume, but takes the shape of the container. 3 B. Its particles are moving rapidly. 3 C. It fills the volume of a container. 1 D. It has particles in a fixed arrangement. 2 E. It has particles close together that are mobile. 60