Energy and States of Matter
Heating and Cooling Curves
Heating Curve for Water
120 °C
steam
water  steam
100 °C
50°C
0 °C
-10 °C
liquid water
ice liquid
ice
Heat added 
Reading a Heating Curve
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
Solution
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
Temperature Changes
T1
beginning temp.1
T1
Tf
final temp of both
T°C
T2
T2
final temp. 2
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.
Heating and Cooling
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
2) absorbed
D. Freezing is
1) endothermic
2) exothermic
Solution
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
Is it Exothermic or Endothermic?
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
Solution
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
Exothermic or Endothermic?
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
Solution
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
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?
Combining Heat Calculations
Step 1: Diagram the change of state
37°C
T = 37.0°C - 0°C = 37.0°C
0°C
S
L
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
Total: Step 2 + Step 3
= 418,000 J
= 611,000 J
+ 193,000 J
Understanding Heat
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
Solution
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