Ch 18: Heat and TemperatureSee all chapters
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Changes in Phase & Latent Heat

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Concept #1: Phase Changes and Latent Heat

Practice: You have an unknown substance, X, which you want to measure the latent heat for. You find that it requires 1.7 x 106 J of heat to completely evaporate 5 moles of substance X. If substance X has a molecular mass of 225 g/mol, what is 𝐿𝑋,𝑒𝑣𝑎𝑝?

Example #1: Finding Information About Heat Changes in Data

Additional Problems
A beaker of negligible mass contains 0.700 kg of water at a temperature of 62.0°C. Mass m of ice at an initial temperature of 0°C is put into the water. After the system has reached thermal equilibrium, all of the ice has melted and the system is all liquid water at 28.0°C. What was the mass m of the ice that was added to the water? Note: c  water = 4186 J/kg and Lfusion = 334,000 J/kg for water.
How much heat must be added to 0.00200 kg of ice at T = -60.0°C to produce 0.0020 kg of liquid water at 30.0°C? (Note: For ice, c = 2010 J/(kg•K) and for liquid water c = 4190 J/(kg•K). For water,  Lf = 3.34 x 105 J/kg and Lv = 2.256 x 106 J/kg.) (a) 5000 J (b) 1420 J (c) 1160 J (d) 1030 J (e) 909 J (f) 493 J (g) none of the above answers
How much heat is required to raise the temperature of 10g of ice from -20°C to 120°C? Note that the specific heat of ice is 2.03 J/g°C, the specific heat of water is 4.184 J/g°C, the specific heat of water vapor is 1.996 J/g°C, the latent heat of fusion of water is 334 kJ/kg, and the latent heat of vaporization of water is 2256 kJ/kg. 
Heating a cup of water to near boiling temperature to use for tea takes time. If 300 mL of water at 23oC is heated on 250 W stove, how long will it take for the water to reach 100oC? If the water is left for 1 minute too long, what percentage of the water evaporated by the time you remove the water from the stove? Assume that the stove outputs 250 W of heat. Note that the specific heat of water is 4.184 kJ/kgK and the latent heat of vaporization of water is 2260 kJ/kg.
You apply 15 kJ/min of heat into 4.5 kg of an unknown material, and plot the change in temperature as a function of time. While the material is a solid, you notice that the temperature is rising at a rate of 25oC/min. Then, the temperature remains constant for 8 minutes. After, while the material is a liquid, you notice the temperature rising at 33oC/min.  (a) What is the specific heat of the material while it's a solid? (b) What is the latent heat of the material for fusion? (c) What is the specific heat of the material while it's a liquid?
If a 2x1014 kg comet impacts the ocean at a speed of 10 km/s, and 1% of the comet's impact kinetic energy goes to boiling the water (the other 99% is going to produce waves in the water), what mass of water will be boiled during the impact? Consider the initial temperature of the water to be 10oC, and that the specific heat of the sea water is the same as fresh water, 4.184 J/gK, as well as the heat of vaporization, 2260 J/gK. For comparison, the mass of the Earth's oceans is considered to be on the order of 1021 kg.