Chapter 10
Energy
Section 10.1
The Nature of Energy
Energy
•
Energy is anything that has the ability to
do work or produce heat.
 All chemical and physical changes
result in the matter changing energy.
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Section 10.1
The Nature of Energy
Energy
•
•
Potential energy – stored energy, due to
position or composition.
Kinetic energy – energy of motion, energy
that is being transferred from one object
to another.
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Section 10.1
The Nature of Energy
Law of Conservation of Energy
•
Energy can be converted from one form to
another, but can be neither created nor
destroyed.
 The energy of the universe is
constant—first law of thermodynamics.
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Section 10.1
The Nature of Energy
Energy
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Section 10.2
Temperature and Heat
Temperature
•
A measure of the random motions of the components
of a substance.
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Section 10.2
Temperature and Heat
Heat
•
A flow of energy between two objects due to a
temperature difference between the objects.
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Section 10.3
Exothermic and Endothermic Processes
•
•
System – part of the universe on which we
wish to focus attention.
Surroundings – include everything else in
the universe.
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Section 10.3
Exothermic and Endothermic Processes
•
Endothermic Process:
 Heat flows into a system.
 Absorb energy from the surroundings.
Surroundings
reaction
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Section 10.3
Exothermic and Endothermic Processes
•
Exothermic Process:
 Energy flows out of the system.
 Energy gained by the surroundings is
equal to the energy lost by the system.
Surroundings
reaction
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Section 10.3
Exothermic and Endothermic Processes
Changes in State
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Section 10.3
Exothermic and Endothermic Processes
Concept Check
Classify each process as exothermic or
endothermic. Explain. The system is
underlined in each example.
a)Your hand gets cold when you touch ice.
b)The ice gets warmer when you touch it.
c)Water boils in a kettle being heated on a stove.
d)Water vapor condenses on a cold pipe.
e)Ice cream melts.
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Section 10.5
Measuring Energy Changes
•
The common energy units for heat are the
calorie and the joule.
 calorie (cal) – the amount of energy
(heat) required to raise the temperature
of one gram of water 1oC.
 Joule (J) – 1 calorie = 4.184 joules
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Section 10.5
Measuring Energy Changes
Energy (Heat) Required to Change the Temperature of a
Substance Depends On:
1. The amount of substance being heated
(number of grams).
2. The temperature change (number of
degrees).
3. The identity of the substance.
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Section 10.5
Measuring Energy Changes
Specific Heat Capacity
•
•
Heat capacity is the amount of heat a
substance must absorb to raise its
temperature by 1 °C.
Specific heat = heat capacity of 1 gram of
the substance.
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Section 10.5
Measuring Energy Changes
Specific Heat Capacities of Some Common Substances
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Section 10.5
Measuring Energy Changes
Energy Required for a Reaction or Process:
•
Energy (heat) required, Q = s × m × ΔT
Q = energy (heat) required (J)
s = specific heat capacity (J/°C·g)
m = mass (g)
ΔT = change in temperature (°C)
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Section 10.5
Measuring Energy Changes
Example
Calculate the amount of heat energy (in
joules) needed to raise the temperature of
6.25 g of water from 21.0°C to 39.0°C.
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Section 10.5
Measuring Energy Changes
Exercises
1. A sample of pure iron requires 142 cal of energy to
raise its temperature from 23ºC to 92ºC. What is
the mass of the sample? (The specific heat
capacity of iron is 0.45 J/gºC.)
2. A 100.0 g sample of water at 90.°C is added to a
500.0 g sample of water at 10.°C. Calculate the
final temperature of the water.
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Section 10.5
Measuring Energy Changes
Summary of Topics: Chapter 10
• Energy
• Endothermic, exothermic
– Phase changes
• Heat Capacity
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