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Lesson_1.2_Printable_PPT

Lesson_1.2_Printable_PPT - Heat Capacity and Specific Heat...

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Heat Capacity and Specific Heat Specific heat of a substance is the amount of heat needed to raise the temperature of 1 kg of a substance by 1 K Specific heat is measured in J·kg -1 ·K -1 and is represented by c 4180 J of heat energy is required to raise the temperature of 1 kg of water by 1 K. 1 kg of water requires 4180 J to raise by 1 K Specific heat of water is 4180 J kg -1 K -1
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1 kg of copper requires 390 J to raise by 1 K 390 J of heat energy is required to raise the temperature of 1 kg of copper by 1 K. Specific heat of copper is 390 J kg -1 K -1 Q = mc ∆θ 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 ∆θ = θ 2 θ 1
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Heat Capacity of an object is the amount of heat needed to raise the temperature of the object by 1 K Heat capacity is measured in J·K -1 and is represented by C If m is the mass of an object, then the heat capacity of that object is: C = m c
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Molar heat capacity ( C m ) is the amount of heat required to raise the temperature of 1 mole of a substance by 1 K. If M is the molar mass of a substance, then C m = M c Molar heat capacity is measured in J mol -1 K -1 Since water is H O, its molar mass = 2 2 + 16 = 18 g = 0.018 kg C m for water = 0.018 x 4180 = 75.2 J mol -1 K -1
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specific heat and molar heat capacity 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
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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 used to overcome the intermolecular forces to free molecules from one another so that they are free to move about. This is the time when a solid turns into a liquid.
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During this change of state, the molecules do not speed up, but the extra energy given is used in gaining potential energy. When heat is supplied to a liquid, the translational kinetic energy of its molecules increase, and its temperature increases. This continues until the liquid reaches its boiling point and any additional heat added does not increase the kinetic energy of the molecules, instead it is used to overcome the intermolecular forces to free molecules from one another so that they are free to escape the liquid.
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