Transcript Chapter 1: An Introduction to Chemistry

© 2003 John Wiley and Sons Publishers
Chapter 8: Working with Chemistry
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Market
Food, Fuel, and Energy
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Courtesy Ken Karp
Figure 8.1: Doing work generates heat.
Work
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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.
Energy
Energy
• Makes objects move.
• Makes things stop.
• Is needed to “do work.”
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)
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Figure 8.3: Heat results from the “brisk agitation” of the particles of matter.
Potential Energy
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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
Kinetic Energy
Kinetic energy is the energy of motion. Examples
are:
 Hammering a nail
 Water flowing over a dam
 Working out
 Burning gasoline
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Potential energy.
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Kinetic energy.
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Work.
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)
Forms of Energy
Energy has many forms:
 Mechanical
 Electrical
 Thermal (heat)
 Chemical
 Solar (light)
 Nuclear
Transfer of Heat
 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.
© 2003 John Wiley and Sons Publishers
Figure 8.4: The calorie and the kilocalorie.
Some Equalities for Heat
 Heat is measured in calories or joules.
1 kilocalorie (kcal) = 1000 calories (cal)
1 calorie = 4.184 Joules (J)
1 kJ = 1000 J
Energy and Nutrition
• On nutrition and food
labels, the nutritional
Calorie, written with a
capital C, is used.
• 1 Cal is actually 1000
calories.
1 Calorie = 1 kcal
1 Cal = 1000 cal
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Courtesy Arthur R. Hill/Visuals Unlimited.
Eating: energy in.
Caloric Food Values
• The caloric values for foods indicate the
number of kcal provided by 1 g of each
type of food.
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Energy stored as fat can be recovered to be spent in various ways, including Sumo
wrestling.
Calories in Some Foods
Energy Requirements
• The amount of energy needed each day
depends on age, sex, and physical activity.
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Exercise, one form of energy expenditure.
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.
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Figure 8.6: Energy and the human machine.
• Basal Metabolic Rate (BMR) is the number
of calories your body burns at rest to
maintain normal body functions.
Learning Check
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
Solution
3) 165 kcal
12 g carb x 4 kcal/g
=
48 kcal
x 9 kcal/g =
81 kcal
9.0 g protein x 4 kcal/g =
36 kcal
Total kcal =
165 kcal
9.0 g fat
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 Capacity
02
Constant Pressure
Bomb
Constant-Pressure Calorimetry
No heat enters or leaves!
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Figure 8.5: Preparing to use a calorimeter to measure the amount of heat released
during a chemical reaction.
QUESTION
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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
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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
Identify two sources and two sinks for
atmospheric carbon.
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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?