Download 15 Energy and Chemical Change

15 Energy and Chemical Change
BIGIDEA
Write the Big Idea for this chapter.
Chemical reactions usually absorb or release energy.
Use the “What I Know” column to list the things you know about the Big Idea. Then list the
questions you have about the Big Idea in the “What I Want to Find Out” column. As you read the
chapter, fill in the “What I Learned” column.
W
What I Want to Find Out
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K
What I Know
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L
What I Learned
15 Energy and Chemical Change
1 Energy
2(G), 11(A), 11(B), 11(D)
MAINIDEA
Write the Main Idea for this lesson.
Energy can change form and flow, but it is always conserved.
REVIEW VOCABULARY
Recall the definition of the Review Vocabulary term.
temperature
temperature
a measure of the average kinetic energy of the particles in
a sample of matter
NEW VOCABULARY
Define each New Vocabulary term.
energy
energy
the ability to do work or produce heat
law of conservation of
energy
Chemical potential energy
law of conservation of energy
heat
reaction or physical process, energy can be converted from one form to
calorie
another, but it is neither created nor destroyed
joule
Chemical potential energy
law stating that in any chemical
the energy stored in a substance because
specific heat
of its composition
heat
energy that is in the process of flowing from a warmer object to a
calorie
the amount of heat required to raise the temperature of one
gram of pure water one degree Celsius (1ºC)
joule
SI unit for heat and energy; one joule is equivalent to 0.2390 calories
specific heat
the amount of heat required to raise the temperature of
one gram of a substance by one degree Celsius
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Copyright © McGraw-Hill Education
cooler object
1 Energy (continued)
Use with pages 516–518.
Compare and contrast kinetic energy with potential energy.
Kinetic energy is the energy of motion. Potential energy is energy of the
composition or position of an object.
On the curve below that represents the skier on a ski slope on page 516,
label the place of greatest kinetic energy A, least kinetic energy B,
greatest potential energy C, and least potential energy D.
B
C
A
D
Describe the skier above as a function of the law of conservation of
energy.
Before the skier starts, there is potential energy that is converted to
kinetic energy, then to potential energy as the skier stops. Energy
changes form.
Explain chemical potential energy.
Chemical
potential
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arrangement of its
energy of a substance is a result of the
atoms
and the strength of the chemical bonds
joining the atoms. During some
chemical
reactions, such as burning
fuel
, much of the potential energy may be released as
heat
. Some of the energy may be converted to work, which is a
form of
kinetic
GET IT?
State the law of conservation of energy in your own words.
energy.
Energy may change forms but is never gained or lost.
Science Notebook • Energy and Chemical Change
255
1 Energy (continued)
Use with pages 519–521.
Identify each symbol in the equation for specific heat.
q = c × m × ΔT
q
represents heat absorbed or released
c
represents the specific heat of the substance
m
represents mass of a sample in grams
ΔT
represents a change in temperature
Summarize. Fill in the blanks to help you take notes while you read
Example Problem.
Problem
The temperature of a sample of iron with a mass of 10.0 g changed
from 50.4°C to 25.0°C with the release of 114 J heat. Determine the
specific heat of iron.
1. Analyze the Problem
Known:
Unknown:
energy released = 114 J
ΔT =
specific heat of iron = ?
50.4°C – 25.0°C = 25.4°C
mass of iron =
10.0 g
2. Solve for the Unknown
Write the equation for heat absorption.
q = c × m × ΔT
c=
c=
q
m × ΔT
114 J
(10.0g) (25.4°C)
=0.499 J / (g.°C)
3. Evaluate the Answer
If the values used in the calculations have three significant figures,
the answer must also have three significant figures. The calculated
value matches the value for iron in Table 2.
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Copyright © McGraw-Hill Education
Solve for c.
q = c × m × ΔT
m × ΔT
1 Energy (continued)
REVIEW IT !
7. MAINIDEA Explain how energy changes from one form to another in an exothermic
reaction. In an endothermic reaction.
Chemical potential energy changes to heat in exothermic reactions, and the heat is released. In
endothermic reactions, heat is absorbed and changed to chemical potential energy.
8. Distinguish between kinetic and potential energy in the following examples: two
separated magnets; an avalanche of snow; books on library shelves; a mountain stream;
a stock-car race; separation of charge in a battery.
Two separated magnets illustrate potential energy. In a snow avalanche, positional potential energy
changes to kinetic energy. Books on a shelf illustrate positional potential energy. As water races down
a mountain stream, positional potential energy changes to kinetic energy. In a stock car race,
chemical potential energy changes to kinetic energy. The separation of charge in a battery illustrates
electrical potential energy.
9. Explain how the light and heat of a burning candle are related to chemical potential
energy.
Chemical potential energy, contained in the candle, is changed to energy in the form of light and heat
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and released as the chemical combustion reaction takes place.
10. Calculate the amount of heat absorbed when 5.50 g of aluminum is heated from 25.0°C to 95.0°C.
The specific heat of aluminum is 0.897 J/(g∙°C).
345 J
11. Interpret Data Equal masses of aluminum, gold, iron, and silver were left to sit in the
Sun at the same time and for the same length of time. Use Table 2 to arrange the four
metals according to the increase in their temperatures from largest increase to smallest.
The temperature change is inversely proportional to specific heat: aluminum, iron, silver, gold.
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