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pchem lab2_joule thompson-1.2

pchem lab2_joule thompson-1.2 - Physical Chemistry...

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Physical Chemistry Laboratory Experiment 2: Measurement of the Joule-Thompson Coefficient for Helium and Carbon Dioxide Kathleen Lenau Partners: Zachary Dymek, Alex Sweeney, Dan Levenstein, Dan Thornhill, Philip Connors, Jessica Lebantz, & Jacquelyn Sikora Conducted: January 25, 2011 Submitted: February 3, 2011 Introduction:
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The Joule-Thomson effect describes the behavior of a real gas as it expands from high pressure to low pressure. Unlike an ideal gas, the internal energy and enthalpy of a real gas is dependent on both temperature and pressure, as Joule and Thomson discovered during their experiment when they noted that there is a temperature associated with the expansion of gas when moved from an area of high pressure to an area of low pressure. The main objective of this laboratory experiment is to recreate the experiments conducted by James Prescott Joule and William Thomson in the 1850’s by measuring the change in temperature experienced by CO 2 and He upon expansion through a nozzle. It has been observed that most gases will cool at room temperature as they expand however there are some, such as He, that will warm upon expansion. This laboratory experiment aims to examine the different behaviors CO 2 and He exhibit upon expansion due to the pressure dependence noted by Joule and Thomson. The Joule-Thomson coefficient can be expressed mathematically as: μJT =∂ ∂ lim∆P 0∆T∆PH T PH Using this relationship, a graph of the change in temperature vs. the change in pressure will be created based upon the measurements made in the lab, enabling the Joule-Thomson coefficient to be calculated from the resulting slope. The experiment value obtained for the Joule-Thomson coefficient can then be compared to accepted literature values, as well as the predicted value made from using the van der Waals equation of state: , - μJT 1Cp m2aRT b Materials & Methods: See lab handout (DiMilla, 2011) for a complete procedure and materials list. Materials Multimeter Thermocouples Insulated chamber CO 2 and He tanks – Middlesex Gases and Technologies Inc. Copper tubing Bourdon gauge Frit Procedure Deviations The experiment for CO 2 was not physically conducted due to a bad CO 2 tank. The values used for this report were hand calculated. The pressure was not increased or decreased over a precise period of time; rather it was varied on average over a period of five seconds. Results: The results from the expansion of CO 2 are as follows:
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Table 1: D ata collected during the analysis of CO 2 , where P is the upstream pressure, V multi is the voltage displayed on the multimeter, and V thermo is the voltage at the thermocouples. P upstream (psig) ΔP (psi) V multi (mV) V thermo (µV) ΔT ( C) ̊ 90.000 -90.000 -26.320 -263.200 -6.749 80.000 -80.000 -23.440 -234.400 -6.010 70.000 -70.000 -20.510 -205.100 -5.259 60.000 -60.000 -17.570 -175.700 -4.505 50.000 -50.000 -14.640 -146.400 -3.754 40.000 -40.000 -11.720 -117.200 -3.005 30.000 -30.000 -8.790 -87.900 -2.254 20.000 -20.000 -5.860 -58.600 -1.503 10.000 -10.000 -2.930 -29.300 -0.751 The pressure drop across the frit was calculated for each measured pressure at the upstream side of the frit as follows: ( )=- ∆P psi Pupstream The corrected thermocouple signal was calculated using the equation: ( )=
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