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# chapter11 - Chapter 11 Energy in Thermal Processes...

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Chapter 11 Chapter 11 Energy in Thermal Processes Energy in Thermal Processes

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U = Q - P D V Vocabulary, 3 Kinds of Energy Vocabulary, 3 Kinds of Energy Internal Energy U = Energy of microscopic motion and inter-molucular forces Work W = -F x = -P V is work done by compression (next chapter) Heat Q = Energy transfer from microscopic contact next chapter
Q = μχ Τ Temperature and Specific Heat Temperature and Specific Heat Add energy -> T rises Property of material Mass

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Example 11.1 Example 11.1 Bobby Joe drinks a 130 “calorie” can of soda. If the efficiency for turning energy into work is 20%, how many 4 meter floors must Bobby Joe ascend in order to work off the soda and maintain her 55 kg mass? N floors = 50.4
Example 11.2 Example 11.2 Aluminum has a specific heat of .0924 cal/gºC. If 110 g of hot water at 90 ºC is added to an aluminum cup of mass 50 g which is originally at a temperature of 23 ºC, what is the final temperature of the equilibrated water/cup combo? T = 87.3 ºC

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Q = μΛ Phase Changes and Latent Heat Phase Changes and Latent Heat T does not rise when phases change (at constant P) Examples: solid -> liquid (fusion), liquid -> vapor (vaporization) Latent heat = energy required to change phases Property of substance /transition
Example 11.3 Example 11.3 1.0 liters of water is heated from 12 ºC to 100 ºC, then boiled away. a) How much energy is required to bring the water to boiling? b) How much extra energy is required to vaporize the water? c) If electricity costs \$75 per MW-hr, what was the cost of heating and boiling the water? a) Q = 8.8x10 4 cal = 3.68x10 5 J b) Q = 5.4x10 5 cal = 2.26x10 6 J c) 5.5 ¢

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Example 11.4 Example 11.4 Consider Bobby Joe from the previous example. If the 80% of the 130 kcals from her soda went into heat which was taken from her body from radiation, how much water was perspired to maintain her normal body temperature? (Assume a latent heat of vaporization of 540 cal/g even though T = 37 ºC) = 193 g A can of soda has ~ 325 g of H 2 0
Three Kinds of Heat Transfer

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