Chapter 8: Working with Chemistry Food, Fuel, and Energy © 2003 John Wiley and Sons Publishers...

Chapter 8: Working with Chemistry

Food, Fuel, and Energy

© 2003 John Wiley and Sons Publishers

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Figure 8.1: Doing work generates heat.

© 2003 John Wiley and Sons Publishers

Courtesy Ken Karp

Work is done when You go up stairs. You play soccer. You lift a bag of groceries. You ride a bicycle. You breathe. Your heart pumps blood. Water goes over a dam.

Work

Energy

• Makes objects move.

• Makes things stop.

• Is needed to “do work.”

Energy

Energy

• Energy: is the capacity to do work, or supply heat.

Energy = Work + Heat

• Kinetic Energy: is the energy of motion.

• Potential Energy: is stored energy.

• Thermal Energy is the kinetic energy of

molecular motion (translational, rotational, and

vibrational).

• Thermal energy is proportional to the temperature

Ethermal T(K)

Figure 8.3: Heat results from the “brisk agitation” of the particles of matter.

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Potential energy is energy that is stored for use at a later time. Examples are:

Water behind a dam A compressed spring Chemical bonds in

gasoline, coal, or food

Potential Energy

Kinetic energy is the energy of motion. Examples are:

Hammering a nail

Water flowing over a dam

Working out

Burning gasoline

Kinetic Energy

Potential energy.

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Kinetic energy.

© 2003 John Wiley and Sons Publishers

Courtesy Dan Helms/Duomo Photography, Inc.

Work.

© 2003 John Wiley and Sons Publishers

Courtesy Dan Helms/Duomo Photography, Inc.

Learning Check

Identify the energy as 1) potential or 2) kinetic

A. Roller blading.

B. A peanut butter and jelly sandwich.

C. Mowing the lawn.

D. Gasoline in the gas tank.

Solution

Identify the energy as 1) potential or 2) kinetic

A. Roller blading. (2 kinetic)

B. A peanut butter and jelly sandwich. (1 potential)

C. Mowing the lawn. (2 kinetic)

D. Gasoline in the gas tank. (1 potential)

Energy has many forms: Mechanical Electrical Thermal (heat) Chemical Solar (light) Nuclear

Forms of Energy

Heat energy flows from a warmer object to a colder object.

The colder object gains kinetic energy when it is heated.

During heat flow, the loss of heat by a warmer object is equal to the heat gained by the colder object.

Transfer of Heat

Figure 8.4: The calorie and the kilocalorie.

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Heat is measured in calories or joules.

1 kilocalorie (kcal) = 1000 calories (cal)

1 calorie = 4.184 Joules (J)

1 kJ = 1000 J

Some Equalities for Heat

• On nutrition and food labels, the nutritional Calorie, written with a capital C, is used.

• 1 Cal is actually 1000 calories.1 Calorie = 1 kcal1 Cal = 1000 cal

Energy and Nutrition

Eating: energy in.

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Courtesy Arthur R. Hill/Visuals Unlimited.

• The caloric values for foods indicate the number of kcal provided by 1 g of each type of food.

Caloric Food Values

Energy stored as fat can be recovered to be spent in various ways, including Sumo wrestling.

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Calories in Some Foods

Energy Requirements

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

Exercise, one form of energy expenditure.

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Courtesy Michael Nichols/Magnum Photos, Inc.

Loss and Gain of Weight

• If food intake exceeds energy use, a person gains weight. If food intake is less than energy use, a person loses weight.

Figure 8.6: Energy and the human machine.

© 2003 John Wiley and Sons Publishers

• Basal Metabolic Rate (BMR) is the number of calories your body burns at rest to maintain normal body functions.

A cup of whole milk contains 12 g of carbohydrates, 9.0 g of fat, and 9.0 g of protein. How many kcal (Cal) does a cup of milk contain?

1) 48 kcal

2) 81 kcal

3) 165 kcal

Learning Check

3) 165 kcal

12 g carb x 4 kcal/g = 48 kcal

9.0 g fat x 9 kcal/g = 81 kcal

9.0 g protein x 4 kcal/g = 36 kcal

Total kcal = 165 kcal

Solution

Calorimetry and Heat Capacity

• Calorimetry is the science of measuring heat changes • for chemical reactions. There are two types of

calorimeters:

• Bomb Calorimetry: A bomb calorimeter measures the heat

change at constant volume such that

• Constant Pressure Calorimetry: A constant pressure calorimeter

measures the heat change at constant pressure such that

Calorimetry and Heat Capacity02

Constant Pressure Bomb

Constant-Pressure Calorimetry

No heat enters or leaves!

Figure 8.5: Preparing to use a calorimeter to measure the amount of heat released during a chemical reaction.

© 2003 John Wiley and Sons Publishers

Courtesy Custom Medical Stock Photo

© 2003 John Wiley and Sons Publishers

What fuel does a candle use to produce its energy? When a car runs out of fuel, the car stops. What happens when a lit candle runs out of fuel? What happens when an animal runs out of its fuel?

QUESTION

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Imagine a child swinging on a playground swing. At what point(s) does the child have the greatest amount of kinetic energy? The greatest amount of potential energy?

QUESTION

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Applying Bacon’s theories of heat in a modern context, suppose you have a cold piece of copper and a hot piece of copper. Using terminology of modern chemistry, what would you say is moving more “briskly” in the hot piece of copper than in the cold one?

QUESTION

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How many kilocalories of work did Count Rumford do simply in heating the 12 kg of water from (let’s assume) 20°C to 100 °C in his two and a half hours of boring work?

QUESTION

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How many joules of work did Count Rumford do in raising the temperature of 12 kg of water from 20 °C to 100 °C? For how many hours would this much energy keep a 40-watt light bulb glowing at full brightness?

QUESTION

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How much energy would you expect to be released by the combustion of hexane, using the same number of molecules of hexane as were used for each of the alkanes of Table 8.1?

QUESTION

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To continue the analogy between the human engine and a car’s engine, what’s the human equivalent to filling a car’s tank with gasoline?

QUESTION

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How many calories are there in 0.1 Calorie? How many Calories are there in 0.1 calorie?

QUESTION

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The population of the entire world is estimated at about 6 billion people. (a) Assuming that the average person spends 200 Calories an hour in the activities of exercise throughout the day, calculate the annual energy output, through exercise alone, by all the humans in the entire world. (b) Calculate the annual average daily use of energy through basal metabolism alone, again by all the humans in the entire world. Assume an average body weight of 50 kg.

QUESTION

© 2003 John Wiley and Sons Publishers

The nutrition information panel on a can of a typical commercial chicken noodle soup reveals that one serving contains 13g of protein, 15g of carbohydrates, and 5g of fat. (a) How many Calories does one serving of this soup provide? (b) What percentage of these Calories comes from fat? (c) How many hours of basal metabolic activity would one serving provide to the average person of the Question at the end of Section 8.9?

QUESTION

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(a) Identify one means of generating electricity that’s driven directly or indirectly by the energy of solar radiation. (b) Identify one that is not.

QUESTION

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What is the source of the energy that drives the process of photosynthesis? Into what form of energy is this transformed within plants?

QUESTION

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Identify two sources and two sinks for atmospheric carbon.

QUESTION

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What two conditions or effects are responsible for a much higher surface temperature on Venus than on Earth? What two conditions or effects are responsible for a much lower surface temperature on Mars?

QUESTION

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If Earth’s average surface temperature keeps increasing at the same rate as for the last quarter of the 20th century, what level will it reach in the year 2100?

QUESTION