SM_chapter17

SM_chapter17 - Energy in Thermal Processes The First Law of...

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461 Energy in Thermal Processes: The First Law of Thermodynamics CHAPTER OUTLINE 17.1 Heat and Internal Energy 17.2 Specific Heat 17.3 Latent Heat and Phase Changes 17.4 Work in Thermodynamic Processes 17.5 The First Law of Thermodynamics 17.6 Some Applications of the First Law of Thermodynamics 17.7 Molar Specific Heats of Ideal Gases 17.8 Adiabatic Processes for an Ideal Gas 17.9 Molar Specific Heats and the Equipartition of Energy 17.10 Energy Transfer Mechanisms in Thermal Processes 17.11 Context Connection Energy Balance for the Earth ANSWERS TO QUESTIONS Q17.1 Temperature is a measure of molecular motion. Heat is energy in the process of being transferred between objects by random molecular collisions. Internal energy is an object’s energy of random molecular motion and molecular interaction. Q17.2 The T is twice as great in the ethyl alcohol. Q17.3 The final equilibrium temperature will show no significant increase over the initial temperature of the water. Q17.4 Some water may boil away. You would have to very precisely measure how much, and very quickly measure the temperature of the steam; it is not necessarily 100 ° C . Q17.5 Heat is energy being transferred, not energy contained in an object. Further, a large-mass object, or an object made of a material with high specific heat, can contain more internal energy than a higher- temperature object. Q17.6 There are three properties to consider here: thermal conductivity, specific heat, and mass. With dry aluminum, the thermal conductivity of aluminum is much greater than that of (dry) skin. This means that the internal energy in the aluminum can more readily be transferred to the atmosphere than to your fingers. In essence, your skin acts as a thermal insulator to some degree (pun intended). If the aluminum is wet, it can wet the outer layer of your skin to make it into a good conductor of heat; then more internal energy from the aluminum can get into you. Further, the water itself, with additional mass and with a relatively large specific heat compared to aluminum, can be a significant source of extra energy to burn you. In practical terms, when you let go of a hot, dry piece of aluminum foil, the heat transfer immediately ends. When you let go of a hot and wet piece of aluminum foil, the hot water sticks to your skin, continuing the heat transfer, and resulting in more energy transfer to you!

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462 Energy in Thermal Processes: The First Law of Thermodynamics Q17.7 Write 1 000 1 1 3 1 000 1 kg 4186 J kg C C kg m J kg C C 3 ⋅° ° = ⋅° ° b ga f e j b ga f V . to find V = × 3 2 10 3 3 . m . Q17.8 (a) and (b) both increase by minuscule amounts. Q17.9 If the system is isolated, no energy enters or leaves the system by heat, work, or other transfer processes. Within the system energy can change from one form to another, but since energy is conserved these transformations cannot affect the total amount of energy. The total energy is constant.
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• Fall '07
• MahaAshour-Abdalla

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