L> General Physics II
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Ch20; Heat and the First Law of Thermodynamics Latent Heat Crystalline materials adjust phase -- melt and freeze or vaporize and condense -- at a solitary, addressed temperature. Energy is compelled for a adjust of phase of a substance. The ratio of the energy to the mass of the substance affiliated is called the latent warmth of the substance. This is a lot choose the certain warm we have actually simply discussed. It is called latent warmth bereason there is no adjust or difference in temperature. Q = m L


You are watching: Latent heat of fusion of ice j/kg

Latent warmth of fusion Lf defines the warmth vital to melt (or freeze) a unit mass of a substance. Latent warm of vaporization Lv defines the warmth crucial to vaporize (or condense) a unit mass of a substance.

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We have already watched Q = c m T For a readjust of state, we now have actually Qf = m Lf and also Qv = m Lv Now, for the fun part! Determining the Equilibrium Temperature We are currently all set to take the concepts of this area and make some amazing calculations or beneficial predictions. This is however another instance of power conservation. For a thermally isolated system, warm might circulation from one object to one more however the complete warm circulation need to be zero. That is vital. For a system of 2 object, this suggests Q1 + Q2 = 0 If tbelow is no change of state, this indicates Q1 = c1 m1 T1 = c1 m1 ( Tf - T1i ) Q2 = c2 m2 T2 = c2 m2 ( Tf - T2i ) Mix 0.15 kg of 10oC milk right into 0.6 kg of 95oC coffee. Both are basically water via a certain warmth capacity of 4186 J/(kg Co). What is the equilibrium temperature? If tright here is a adjust of state, we must incorporate the latent heats involved. Q = c m T + m L or also Q = c1 m T + m L + c2 m T There is no single "basic equation" to memorize. The finest point -- the only thing -- to execute is to understand also that this is simply energy conservation and look at all the processes that reason warmth loss and also all the processes that cause warm obtain. Set those 2 equal to each other -- or set the amount of them equal to zero. Let"s make some iced tea! Stir 0.25 kg of ice, initially at - 5oC, into 0.5 kg of tea, initially at 45oC. What is the final temperature? The certain heat of (liquid) water is cw = 4186 J/(kg Co). The warmth of fusion for ice or water is Lf = 3.33 x 105 J/kg. The certain warm of (frozen) ice is ci = 2090 J/(kg Co).

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Notice that the specific heat is different for ice and also water! Working many type of examples is the ideal means to become comfortable with Equilibrium Temperature difficulties.
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Heat Capacity Work and also Heat Rerotate to Ch20 ToC (c) Doug Davis, 2002; all civil liberties reserved