L,AmN=CCnm2△T (4) Thus, we get: △T where Lv =Latent heat of vaporization of liquid nitrogen mcu= Mass of the copper cylinder immersed into liquid nitrogen CCu Specific heat of copper in the temperature range from room temperature to the (-1958℃) Initial te of the copp TAcu =Final temperature of the copper cylinder at the B P.T. of LN (-195.8C) Amin Mass of liquid nitrogen evaporated by the immersion of the copper cylinder Since the specific heat of copper in this big range(-195.8C-room temperature) is not a constant, we introduce another way to calculate the total heat energy transferred to liquid nitrogen by the copper cylinde The first part: when the copper cylinder has the same temperature with the liquid nitrogen (i.e, theyre in thermal equilibrium), quickly move the copper cylinder into a cup of water; as the copper now is at a very low temperature(-195.8C), it will absorb energy form the"hot "water and then they will be in thermal equilibrium. In order to avoid the background energy contribution, you should use the copper stirrer to speed up the energy transfer process, and the lowest value of should be the thermal equilibrium temperature. The energy transferred from water to copper is as follow Q=(mcn+mc+mc+h)(2-3)=macm2-(-1958) Cw Specific heat of water ma=Mass of the small aluminum cup Ca= Specific heat of aluminum me=mass of the copper stirrer Ce = Specific heat of copper in the temperature range from h to B3, it's almost constant e2 Initial temperature of water and aluminum cup 83= Final temperature of the system(water, aluminum cup and copper cylinder) ht =0, hr means the thermal capacity of the part of the electric thermometer which is immersed under water. In our lab. this value can be considered to be small enough to be neglected. The second part: the energy needed by the copper cylinder whose temperature increases from 83 to 01(the initial temperature: room temperature)
15 L m C m T v LN Cu Cu . (4) Thus, we get: , , ( ) Cu Cu Cu Cu Cu i Cu f Cu v LN LN C m T C m T T L m m (5) where： Lv = Latent heat of vaporization of liquid nitrogen mCu = Mass of the copper cylinder immersed into liquid nitrogen. CCu = Specific heat of copper in the temperature range from room temperature to the temperature of liquid nitrogen (-195.8℃) Ti,Cu = Initial temperature of the copper cylinder: room temperature. Tf,Cu = Final temperature of the copper cylinder at the B.P.T. of LN (-195.8℃). ∆mLN = Mass of liquid nitrogen evaporated by the immersion of the copper cylinder. Since the specific heat of copper in this big range (-195.8℃~room temperature) is not a constant, we introduce another way to calculate the total heat energy transferred to liquid nitrogen by the copper cylinder. The first part: when the copper cylinder has the same temperature with the liquid nitrogen (i.e, they're in thermal equilibrium), quickly move the copper cylinder into a cup of water; as the copper now is at a very low temperature(-195.8℃), it will absorb energy form the “hot” water and then they will be in thermal equilibrium. In order to avoid the background energy contribution, you should use the copper stirrer to speed up the energy transfer process, and the lowest value of the thermometers should be the thermal equilibrium temperature. The energy transferred from water to copper is as follow: 1 2 3 3 [ ( 195.8)] Q m c m c m c h m c w w a a c c t cu cu (6) where： mw = Mass of the water. cw = Specific heat of water. ma = Mass of the small aluminum cup. Ca = Specific heat of aluminum. mc = mass of the copper stirrer. cc = Specific heat of copper in the temperature range from θ2 to θ3, it’s almost constant. θ2 = Initial temperature of water and aluminum cup. θ3 = Final temperature of the system (water, aluminum cup and copper cylinder). ht = 0，ht means the thermal capacity of the part of the electric thermometer which is immersed under water. In our lab, this value can be considered to be small enough to be neglected. The second part: the energy needed by the copper cylinder whose temperature increases from θ3 to θ1 (the initial temperature: room temperature)
(G-a) where meu Mass of the copper cylinder immersed into liquid nitrogen Ceu=Specific heat of copper in the temperature range from O1 to 63, it's almost constant B1 Initial temperature of the copper cylinder: room temperature 63 = Final temperature of the system(water, aluminum cup and copper cylinder) So the Latent heat of vaporization of liquid nitrogen can be written as follow 1[mc+m2+m+h)(9-9)+m(- Experimental apparatus 1. Electric thermometers 2. Copper cylinder 3. Water 4.Warm cup 5. Stop watch 6. Electric balance 7. Liquid nitrogen Procedure 6)Measurement of the Latent Heat of Vaporization of Liquid Nitrogen Measure and record the mass(mcu) of the copper cylinder which will be placed in liquid nitrogen Put liquid nitrogen into the warm isolated cup to 2/3 full Put the cup and the copper cylinder on the electron balance as shown in the figure right. Start the timer and record the time duration for each mass reduction of 0.5 gram, you should record at least six sets of data Put the copper cylinder into the liquid nitrogen(write down this moment as tb). Observe the phenomenon and record in detail Do not stop the watch
16 Q m c 2 1 3 cu cu (7) where： mcu = Mass of the copper cylinder immersed into liquid nitrogen. ccu = Specific heat of copper in the temperature range from θ1 to θ3, it’s almost constant. θ1 = Initial temperature of the copper cylinder: room temperature. θ3 = Final temperature of the system (water, aluminum cup and copper cylinder). So the Latent heat of vaporization of liquid nitrogen can be written as follow: 2 3 1 3 1 v w w a a c c t cu cu LN L m c m c m c h m m c (8) Experimental Apparatus 1. Electric thermometers 2. Copper cylinder 3. Water 4. Warm isolated cup 5. Stop watch 6. Electric balance 7. Liquid nitrogen Procedure 6) Measurement of the Latent Heat of Vaporization of Liquid Nitrogen Measure and record the mass (mCu) of the copper cylinder which will be placed in liquid nitrogen. Put liquid nitrogen into the warm isolated cup to 2/3 full. Put the cup and the copper cylinder on the electron balance as shown in the figure right. Start the timer and record the time duration for each mass reduction of 0.5 gram, you should record at least six sets of data. Put the copper cylinder into the liquid nitrogen (write down this moment as tb). Observe the phenomenon and record in detail. Do not stop the watch