1. Chapter 17 Thermochemistry 17.1 The Flow of Energy
17.2 Measuring and Expressing
Enthalpy Changes
17.3 Heat in Changes of State
17.4 Calculating Heats of Reaction
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2. Why does lava cool faster in water than in air?
CHEMISTRY & YOU
Why does lava cool faster in water than in air?
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3. Water requires _________ _____________________.
CHEMISTRY & YOU
Heat will flow from the lava to the surroundings until the lava and surroundings are at the same temperature. Air has a smaller ________________ than water. Why would lava then cool more quickly in water than in air?
Water requires _________ _____________________.
Therefore, lava in contact with water loses more heat energy than lava in contact with air, allowing it to cool more quickly.
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4. Energy Transformations
Energy is ____________________________ ___________________________________. .
Unlike matter, energy has neither mass nor volume.
Energy is detected only because of its effects.
Thermochemistry is __________________ _______________________________________________________________________.
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5. Energy Transformations
Every substance has a certain amount of _____________ stored inside it.
The energy stored in the chemical bonds of a substance is called _________________ _________________.
The kinds of atoms and the arrangement of the atoms in a substance determine the amount of energy stored in the substance.
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6. Energy Transformations
Energy changes occur as either heat transfer or work, or a combination of both.
Heat, represented by q, is energy that transfers from one object to another because of a temperature difference between the objects.
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7. Energy Transformations
Heat flows spontaneously from _________ __________________________________.
If two objects remain in contact, heat will flow from the warmer object to the cooler object until the temperature of both objects is the same.
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8. D. chemical potential energy.
The energy released when a piece of wood is burned has been stored in the wood as
A. sunlight.
B. heat.
C. calories.
D. chemical potential energy.
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9. Endothermic and Exothermic Processes
What happens to the energy of the universe during a chemical or physical process?
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10. Endothermic and Exothermic Processes
What happens to the energy of the universe during a chemical or physical process?
Chemical reactions and changes in physical state generally involve either the ____________________________.
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11. Endothermic and Exothermic Processes
You can define a __________ as the part of the universe on which you focus your attention.
Everything else in the universe makes up the _________________.
Together, the system and its surroundings make up the universe.
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12. Endothermic and Exothermic Processes
The law of conservation of energy states that in any chemical or physical process, energy is neither created nor destroyed.
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13. Endothermic and Exothermic Processes
During any chemical or physical process, the energy of the universe _____________________.
If the energy of the system increases during that process, the energy of the surroundings must decrease by the same amount.
If the energy of the system decreases during that process, the energy of the surroundings must increase by the same amount.
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14. Endothermic and Exothermic Processes
Direction of Heat Flow
The direction of heat flow is given from the point of view of the system.
Heat is absorbed from the surroundings in an _____________________________.
Heat flowing into a system from its surroundings is defined as positive; q has a positive value.
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15. Endothermic and Exothermic Processes
Direction of Heat Flow
The direction of heat flow is given from the point of view of the system.
An ______________________ is one that releases heat to its surroundings.
Heat flowing out of a system into its surroundings is defined as negative; q has a negative value.
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16. Endothermic and Exothermic Processes
In an endothermic process, heat flows into the system from the surroundings.
In an exothermic process, heat flows from the system to the surroundings.
In both cases, energy is __________________.
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17. Endothermic and Exothermic Processes
Units for Measuring Heat Flow
Heat flow is measured in two common units:
the calorie
the joule
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18. Endothermic and Exothermic Processes
Units for Measuring Heat Flow
A calorie (cal) is defined as the quantity of heat needed to raise the temperature of 1 g of pure water 1°C.
The word calorie is written with a small c except when referring to the energy contained in food.
The dietary Calorie is written with a capital C.
One dietary Calorie is equal to one kilocalorie, or 1000 calories.
1 Calorie = 1 kilocalorie = 1000 calories
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19. Endothermic and Exothermic Processes
Units for Measuring Heat Flow
The joule (J) is the SI unit of energy.
One joule of heat raises the temperature of 1 g of pure water °C.
You can convert between calories and joules using the following relationships:
1 J = cal
4.184 J = 1 cal
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20. Athletes often use instant cold packs to soothe injuries
Athletes often use instant cold packs to soothe injuries. Many of these packs use the dissociation of ammonium nitrate in water to create a cold-feeling compress. Is this reaction endothermic or exothermic? Why?
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21. Heat Capacity and Specific Heat
On what factors does the heat capacity of an object depend?
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22. Specific Heats of Some Common Substances
Interpret Data
The specific heat capacity, or simply the specific heat, of a substance is the ____________________ _________________________________________.
Water has a very high specific heat compared with the other substances.
Metals generally have low specific heats.
Specific Heats of Some Common Substances
Substance
Specific heat
J/(g·°C)
cal/(g·°C)
Liquid water
4.18
1.00
Ethanol
2.4
0.58
Ice
2.1
0.50
Steam
1.9
0.45
Chloroform
0.96
0.23
Aluminum
0.90
0.21
Iron
0.46
0.11
Silver
0.24
0.057
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23. Heat Capacity and Specific Heat
Calculating Specific Heat
To calculate the specific heat (C) of a substance, you divide the heat input by the mass of the substance times the temperature change.
C = q
m  ΔT =
mass (g)  change in temperature (oC)
heat (J or cal)
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24. Heat Capacity and Specific Heat
Calculating Specific Heat
C = q
m  ΔT =
mass (g)  change in temperature (°C)
heat (J or cal)
q is _____, expressed in terms of joules or calories.
m is ___________.
ΔT is the change in temperature.
________________
The units of specific heat are either J/(g·°C) or cal/(g·°C).
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25. Calculating the Specific Heat of a Substance
Sample Problem 17.2
Calculating the Specific Heat of a Substance
The temperature of a 95.4-g piece of copper increases from 25.0°C to 48.0°C when the copper absorbs 849 J of heat. What is the specific heat of copper?
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26. Calculate Solve for the unknown.
Sample Problem 17.2
Calculate Solve for the unknown. 2
Start with the equation for specific heat.
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27. Calculate Solve for the unknown.
Sample Problem 17.2
Calculate Solve for the unknown. 2
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28. Evaluate Does the result make sense?
Sample Problem 17.2
Evaluate Does the result make sense? 3
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29. Key Concepts & Key Equation
Energy changes occur as either heat transfer or work, or a combination of both.
During any chemical or physical process, the energy of the universe remains unchanged.
The heat capacity of an object depends on both its mass and its chemical composition.
C = q
m  ΔT
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30. chemical potential energy: energy stored in chemical bonds
Glossary Terms
thermochemistry: the study of energy changes that occur during chemical reactions and changes in state
chemical potential energy: energy stored in chemical bonds
heat (q): energy that transfers from one object to another because of a temperature difference between the objects
system: a part of the universe on which you focus your attention
surroundings: everything in the universe outside the system
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31. endothermic process: a process that absorbs heat from the surroundings
Glossary Terms
law of conservation of energy: in any chemical or physical process, energy is neither created nor destroyed
endothermic process: a process that absorbs heat from the surroundings
exothermic process: a process that releases heat to its surroundings
heat capacity: the amount of heat needed to increase the temperature of an object exactly 1°C
specific heat: the amount of heat needed to increase the temperature of 1 g of a substance 1°C; also called specific heat capacity
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32. BIG IDEA
Matter and Energy
During a chemical or physical process, the energy of the universe is conserved.
If energy is absorbed by the system in a chemical or physical process, the same amount of energy is released by the surroundings.
Conversely, if energy is released by the system, the same amount of energy is absorbed by the surroundings.
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33. END OF 17.1
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