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lecture notes-Chapter14-posted

# lecture notes-Chapter14-posted - Chapter 14 Heat Internal...

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1 Chapter 14: Heat Internal Energy Heat Heat Capacity Specific Heat Phase Transitions Thermal Conduction Thermal Convection Thermal Radiation

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2 §14.1 Internal Energy The internal energy of a system is the sum total of all the energy of all the molecules in the system. It does not include macroscopic kinetic energy nor energy due to external interactions (potential energy).
3 Internal energy includes: Translational and rotational kinetic energy of the particles due to their individual motions. Vibrational kinetic and potential energy Potential energy due to interactions between particles in the system. Chemical and nuclear energy (binding energies)

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4 Internal energy does not include: The kinetic energy of the molecules due to translations, rotations, and vibrations of the whole or large fraction of the system. Potential energy due to the interactions of the molecules of the system with bodies outside of the system (external interactions).
5 Example (text problem 14.5): A child of mass 15 kg climbs to the top of a slide that is 1.7 m above a horizontal run that extends for 0.5 m at the base of the slide. After sliding down, the child comes to rest just before reaching the very end of the horizontal portion of the slide. How much internal energy was generated during this process? 1.7 m U = 0 KE = 0 U = mgh KE = 0

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6 Example continued: The change in mechanical energy of the child is E= E f – E i = -mgh = -250 J. This is the increase in internal energy and is distributed between the child, the slide, and the air.
7 §14.2 Heat Heat is energy in transit between two systems at different temperatures. Heat flows from the system at high temperature to the system at low temperature.

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8 An experiment by Joule showed that the quantity of work done on a system or the same quantity of heat flowing into a system causes the same increase in the system’s internal energy. Heat is measured in joules or calories. 1 cal = 4.186 J (the mechanical equivalent of heat); 1 Calorie (used on food packaging) = 1 kcal.
9 §14.3 Heat Capacity and Specific Heat For many substances, under normal circumstances T Q. Or Q = C T where C is the heat capacity . The specific heat capacity, or just specific heat, of a substance is the heat capacity per unit mass. T m Q m C c = = or T mc Q = Think of heat capacity as a measure of how much heat must flow into or out of the system to produce a given temperature change.

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10 Example (text problem 14.12): If 125.6 kJ of heat are supplied to 5.00 × 10 2 g of water at 22 ° C, what is the final temperature of the water? ( 29 ( 29 ( 29 C 82 C kJ/kg 186 . 4 kg 5 . 0 kJ 125.6 C 22 i f i f ° = ° + ° = + = - = = mc Q T T T T mc T mc Q
11 Example (text problem 14.19): A 0.400 kg aluminum teakettle contains 2.00 kg of water at 15.0 ° C. How much heat is required to raise the temperature of the water (and kettle) to 100 ° C?

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