Lesson 1.2
Heat Capacity and Specific Heat
Lesson Objectives:
At the end of this lesson students will be able to describe the concepts of heat
capacity, specific heat and latent heat and use them to solve problems from
everyday life.
1.
Specific Heat Capacity.
Specific heat of a substance is the amount of heat needed to
raise the temperature of 1 kg of a substance by 1 K
It is measured in JKg
1
K
1
and is represented by C. The quantity of heat Q
required to raise the temperature of m kg of a substance from an initial
temperature
θ
1
to a final temperature
θ
2
is given by
Q
=
m C
∆θ
….1
Where C is its specific heat capacity and
∆θ
=
θ
2
–
θ
1
4180 J of heat energy is required to raise the temperature of 1 kg of water by
1 K. Therefore, the specific heat of water is 4180 JKg
1
K
1
= 4.18 kJKg
1
K
1
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View Full DocumentMolar specific heat (C
m
)is the amount of heat required to raise the
temperature 1 mole of a substance by 1 K.
If M is the molar mass of a substance, then:
C
m
= M C
…2
Table 1 below gives the specific heats and the molar specific heats of some
common substances.
Substance
C
(J.kg
1
.K
1
)
C
m
(J.mol
1
.K
1
)
Aluminum
900
24.3
Alcohol (ethyl)
2400
111
Copper
390
24.5
Glass
840
Iron
450
25.2
Lead
130
26.4
Silver
230
24.9
Water (20
o
C)
4180
75.2
Ice(10
o
C)
2050
36.9
Since water is H
2
O, its molar mass
=
2 + 16
= 18 g = 0.018 kg
Therefore, C
m
for water = 0.018 × 4180 = 75.2
Jmol
1
K
1
Specific heat of a substance can be measured by using the principle of
method of mixtures.
When hot objects are mixed with cold objects, the hot
objects lose heat and the cold objects gain heat until the
system reaches thermal equilibrium. If the system is
insulated
,
the amount of heat lost by the hot objects = the amount of
heat gained by the cold objects.
2.
Latent Heat and Change of State.
When heat is supplied to a solid, the vibrational kinetic energy of its
molecules increase, and hence the temperature of the solid increases. This
continues until the solid reaches its melting point and any additional heat
added does not increase the kinetic energy of the molecules, instead it is
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 Spring '11
 George
 Physics, Thermodynamics, Heat, 50 g, 18 g, 20 g, 104 M, 106 J

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