Brendan MullanPhysics 152 Section LUHasbrouck Room 204December 9, 2015Experiment 6: Latent Heat of Vaporization of Liquid Nitrogen

Abstract: In this lab, we were observing liquid nitrogen. We were attempting to measure its latent heat of vaporization. To do this, we measured the time it took for the liquid nitrogen to evaporate to different masses. We conducted this process twice, once without a resistor in the liquid nitrogen and once with the resistor in the liquid nitrogen. Then we used these measured values to calculate Lv, the latent heat of vaporization.Questions:1. Latent heat of vaporization is the amount of energy released as a system goes from liquid to gas. Phase change is a change from one phase to another without changing the chemical makeup of the system. The latent heat of vaporization for liquid nitrogen is 201 J/G. Source: http://physics.tutorvista.com/heat/latent-heat.html2. Lv = = [(Volt)*(Amp)]/[(g/sec)-(g/sec)] = [()*(A)]/ [(g/sec)-(g/sec)] = ()*( = (* ( = .3. V = 25.5 Volts, I = 0.712 Amps. No the rate of evaporation was never a constant. It was usually close to a constant but never constant. You can tell by calculating (dm/dt) for each situation.4. i.) Average Lv = / total number of Lv = 171.1123 J/g. ii.) Standard Deviation Lv = 26.51365. iii.) Percent difference = .5. No it was not necessary to zero the balance scale because it was not necessary to calculate the exact mass but rather the difference between the masses.6. a.) Energy = (280 J/g) * (6 g) = 1680 J. b.) Power (W) = Energy (J) / time (s)100 W = 100 J/sEnergy = (280 J/g) * (5 g) = 1400 JTime = Energy/Power = 1400 J / 100 J/s = 14 seconds.7. Yes because when the steam hits your body, it first has to convert to liquid water. This conversion releases more energy than just the water hitting your body, therefore resulting in a more severe burn.8. a.) The phenomenon that began at t1 and ended at t2 is the water boiling from its liquid state to its gaseous state. b.) The water is at 100 degress C. c.) The water is in its gaseous state after t2.Conclusion:In this lab, we were attempting to calculate the latent heat of vaporization of liquid nitrogen. We used a balance, a cup of liquid nitrogen, a resistor and a timer to complete this experiment. We took down the mass and the time at different points throughout two different trials. Then we used these measurements to calculate Lv at different points, and then calculated an average value. My average was 171.1123 J/g, which is only about 15% different from the true value of 201 J/g. So in conclusion, we came close to the true value and the difference can be attribute to small error, including human error.