Heating & Cooling Curves
Chapter 6
Energy and States of Matter
Heating and Cooling Curves
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120 °C
100 °C
Heating Curve for Water
water
steam steam
50 °C liquid water
0 °C ice
liquid
-10 °C ice
Heat added
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Learning Check CS1
A. The flat lines on a heating curve represent
1) a temperature change
2) a constant temperature
3) a change of state
B. The sloped lines on a heating curve represent
1) a temperature change
2) a constant temperature
3) a change of state
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Solution CS1
A. The flat lines on a heating curve represent
2) a constant temperature
3) a change of state
B. The sloped lines on a heating curve represent
1) a temperature change
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T °C
Temperature Changes
T(1) beginning temp.1
T(1)
T(f) final temp of both
T(2)
T(2) final temp. 2
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Cooling Curve
Using the heating curve of water as a guide, draw a cooling curve for water beginning with steam at 110 °C and ending at -20 °C.
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Learning Check CS2
A. Water condenses at a temperature of
1) 0 °C 2) 50 °C 3) 100 °C
B. At a temperature of 0 °C, water
1) freezes 2) melts 3) changes to a gas
C. When a gas condenses, heat is
1) released
D. Freezing is
2) absorbed
1 ) endothermic 2) exothermic
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Solution CS2
A. Water condenses at a temperature of
3) 100 °C
B. At a temperature of 0 °C, water
1) freezes 2) melts
C. When a gas condenses, heat is
1) released
D. Freezing is
2) exothermic
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Learning Check CS3
Is energy absorbed (1) or released (2) in each of the following:
____A. Ice to liquid water
____B. Water vapor to rain
____C. Water to ice
When it rains, the air becomes
1) warmer 2) cooler 3) does not change
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Solution CS3
Is energy absorbed (1) or released (2) in each of the following:
_1__ A. Ice to liquid water
_2__ B. Water vapor to rain
_2__ C. Water to ice
When it rains, the air becomes
1) warmer
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Learning Check CS4
Complete using the terms gains or loses
In the cooling coils of a refrigerator, liquid
Freon ___________ heat from the food and changes to a gas
Food ___________heat and becomes colder
In the back of the refrigerator, Freon
_________ heat and condenses back to a liquid
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Solution CS4
Complete using the terms gains or loses
In the cooling coils of a refrigerator, liquid Freon absorbs heat from the food and changes to a gas
Food loses heat and becomes colder
In the back of the refrigerator, Freon loses heat and condenses back to a liquid
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Combining Heat Calculations
To reduce a fever, an infant is packed in 1250 g of ice. If the ice at 0 °C melts and warms to body temperature (37.0
°C) how much heat in joules is absorbed?
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Combining Heat Calculations
Step 1: Diagram the change of state
37 °C
0 °C S L
T = 37.0
°C - 0°C = 37.0°C
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Step 2: Calculate the heat to melt ice
(fusion)
= 1250 g ice x 334 J
1 g ice
= 418,000 J
Step 3: Calculate the heat to warm the water from 0 °C to 37°C
= 1250 g x 37.0
°C x 4.18 J g °C
= 193,000 J
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Total: Step 2 + Step 3
=
418,000 J + 193,000 J
= 611,000 J
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Learning Check CS8
A. Why do drops of liquid water form on a glass of iced tea ?
B. When it snows, the air temperature seems warmer. How can that be?
C. How much heat is needed to change 1.00 g of water at 0 ° to steam at 100°C?
1) 540 cal 2) 640 cal 3) 720 cal
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Solution CS8
A. Why do drops of liquid water form on a glass of iced tea?
Condensation of water in the air that cools
B. When it snows, the air temperature seems warmer. How can that be?
Condensation is exothermic; heat is released.
C. How much heat is needed to change 10.0 g of water at 0 ° to steam at 100°C?
2) 640 cal
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