MODULE 3
21
WORKSHEET
THERMAL PROPERTIES
OF WATER
Syllabus reference 8.4.5
1
Match the statement on left with the most appropriate answer on the right. Write your answer in
the space provided.
a
A measure of the degree of hotness
or coldness of an object.
Temperature
b
The amount of heat required to raise the
temperature of a unit mass of a substance
by 1ºC.
Specific heat capacity
Process that releases heat.
Exothermic
d
Process that absorbs heat.
Endothermic
e
The heat absorbed when one mole of a
substance dissolves in a large excess of
water.
Molar heat of solution
f
Dissolving this chemical results in an
exothermic reaction.
Sodium hydroxide
g
Dissolving this chemical results in an
endothermic reaction.
Potassium nitrate
h
A significant increase in the temperature
of a river or lake due to the discharge of
large quantities of hot water.
Thermal pollution
The effect of increased temperature on the
amount of dissolved oxygen.
Decrease
j
The effect of increased temperature on the
amount of dissolved salts.
Increase
k
Measure of the rate at which a substance
transmits heat from a hot location to a
cooler one.
Thermal conductivity
c
i
Copyright © 2008 McGraw-Hill Australia
Endothermic
Increase
Specific heat capacity
Exothermic
Potassium nitrate
Temperature
Decrease
Molar heat of solution
Thermal conductivity
Sodium hydroxide
Thermal pollution
CONQUERINGCHEMISTRY PRELIM
MODULE 3 WS 21
2
Calculate the quantity of heat needed to raise the temperature of:
a 5.8 g aluminium from 20º to 75º (C = 0.90 J/K/g)
Amount of heat required  5.8  0.90  (75  20)
 287 J
b
2.5 mol sulfur from 25ºC to 85ºC (C = 0.72 J/K/g)
m(S)  2.5  32.1  80.25 g
Amount of heat required  80.25  0.72  (85  25)
 3.5  103 J
c
150 mL water by 28ºC (C = 4.18 J/K/g)
m(H2O)  150  1.00  150 g
Amount of heat required  150  4.18  28
 1.8  104 J
3
To measure the specific heat capacity of tetrachloromethane, a student used a small electrical
immersion heater of negligible heat capacity to heat 70.0 g of the liquid in a well-insulated
polystyrene container (a coffee cup). The heater delivered 1.68 kJ of energy and raised the
temperature of the tetrachloromethane from 18.5ºC to 46.4ºC. Calculate the specific heat capacity
of tetrachloromethane.
Amount of heat  1.68 kJ  1.68  103 J
1.68  103  70.0  C  27.9
C  0.86 J/K/g
4
A group of students was trying to calculate the molar heat of solution of potassium hydroxide.
They dissolved 5.61 g of solid potassium hydroxide in 100 mL of water and found the temperature
change to be 13.0 ºC.
Calculate the molar heat of solution for potassium hydroxide.
Mass  5.61  100  105.61 g
Amount of heat released  105.61  4.18  13.0
 5.74  103 J
n(KOH)  5.61/(39.1  16  1)  0.1 mol
Molar heat of solution  5.74  103/0.1  5.74  104 J  57 kJ
Copyright © 2008 McGraw-Hill Australia
CONQUERINGCHEMISTRY PRELIM
MODULE 3 WS 21
5
When concentrated nitric acid (HNO3) is added to water, 30 kJ of heat is liberated for every mole
of HNO3. What mass of nitric acid is needed to release 3615 kJ of heat?
Mass of 1 mole HNO3  1  14  3  16  63 g
63 g releases 30 kJ
Mass needed  3615/30  63  7.6  103 g  7.6 kg
6
a
Explain what is meant by thermal pollution.
Thermal pollution is the discharge into a lake or river of quantities of hot water that are large
enough to increase significantly the temperature of the water body. A 2 to 5ºC increase can be
significant.
b
Describe a situation in which thermal pollution may occur.
A lake or river is used for cooling in industry or electricity generation. Cooling water is pumped
from the natural water through the factory or power station then discharged back into the lake
or river.
c
List three detrimental effects thermal pollution has on aquatic organisms.
❍ Less dissolved oxygen can stress organisms
❍ Fish eggs do not develop or hatch if the temperature is too high
❍ False temperature cues can set off migration or spawning at the wrong time of the year
❍ Lethal temperature limits may be exceeded
❍ Sudden temperature changes can kill fish eggs
Copyright © 2008 McGraw-Hill Australia
CONQUERINGCHEMISTRY PRELIM
MODULE 3 WS 21