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Lesson_1.2

# Lesson_1.2 - Lesson 1.2 Heat Capacity and Specific Heat...

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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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Molar 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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Lesson_1.2 - Lesson 1.2 Heat Capacity and Specific Heat...

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