Allison Edwards-Thermodynamics (Gas Thermometry)

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Feb 20, 2024

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Experiment #1: Gas Thermodynamics (Gas Thermometry) Allison Edwards CHM3411L 1/23/2024
Introduction This experiment aims to utilize a gas thermometer apparatus to determine the temperatures of two fixed points: the steam point and ice point. The gas thermometer is calibrated to the ice point within the University of Central Florida Physical Chemistry lab using helium gas. In order to accomplish the most accurate results, three measurements are taken for both ice point and steam point. The idea is that once the temperature has been fixed at two or more points, temperatures at other points can be defined within this thermometer range. 1 The perfect gas law, pV = nRT , is taken into consideration for calculations and assembly of the system used in this experiment. Temperatures will be read in Celsius but will be convert to Kelvin by adding the ice point temperature of water to the temperature in Celsius: t ( ) = T ( K ) 273.15 . The molar volume of the gas bulb will be determined using the equation 1 ~ V = n V p 0 RT 0 , where p 0 is the pressure at the ice point, V is the volume of the gas bulb on the gas thermometer, n is the number of moles in the gas, T 0 is the temperature in Kelvin of the ice point, R is the gas constant, and ~ V is the molar volume of the gas bulb. For the purpose of this lab, R will be applied in the units of 62.36 L*Torr*K -1 *mol -1 . The proportionality factor used for the accuracy achieved in this experiment will be A A 0 = 1 + p p 0 p r v V + 3 t 1 ~ V ( B B 0 ) . B is a second virial coefficient, p r is the pressure measured in the lab, and is given for Pyrex glass as 3.2x10 -6 K -1 . 1 The equations used in the experiment will work in conjunction with the pressure and temperature readings obtained within the lab atmosphere. Gas thermometry has been utilized in labs for decades to obtain thermodynamic temperatures. National metrology institutes (NMIs) notably used similar helium-filled gas thermometers. 3 The setup being utilized in this lab is similar to that of a typical research lab. The apparatus is connected to a pressure gauge, via glass and plastic tubing, which will be accounted for in calculations as a cumulative “dead space.” Results of gas thermometer readings are expected to be accurate, and potentially less precise than other methods. Comparing data from this experiment to commonly known theoretical values for the ice point and steam point of water, 273.15 K and 373.15 K, respectively, should support this claim. 2
Procedure The procedure used followed the instructions found in the Gas Thermometry experiment on pages 91-98 of the Experiments in Physical Chemistry textbook. 1 The pressure was adjust to 450 Torr instead of 600 Torr. Results Table 1. Calculated volumes of apparatus Apparatus Volume Bulb (V) 48 cm 3 0.00007 cm 3 Dead Space (v) 247 cm 3 0.0001 cm 3 Table 2. Measured pressures Trial Ice-Point Pressure (p 0 ) Steam-Point Pressure Gas Bulb Pressure at Room Temperature (p r ) 1 420.5 Torr 0.05 Torr 536.7 Torr 0.05 Torr 449.1 Torr 0.01 Torr 2 420.5 Torr 0.05 Torr 535.8 Torr 0.05 Torr 3 419.2 Torr 0.05 Torr 533.7 Torr 0.05 Torr Average 420.1 Torr 0.05 Torr 535.4 Torr 0.05 Torr Table 3. Temperatures Temperature T (K) T ( C) Ice-Point (T 0 ) 273.1 K 0.005 K -0.1 C 0.005 C Steam-Point 348.07 K 0.0005 K 74.9 C 0.005 C Room (T r ) 295.15 K 0.0005 K 22 C 0.05 C Discussion
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The ice-point temperature was found to be 273.1 K with a value of uncertainty of 0.0005 K. The known ice-point of water is 273.15 K. 2 The experimental temperature of the ice-point was off by approximately 0.05 K. The discrepancy could be attributed to the degree of uncertainty, but is indicative of a properly functioning gas thermometer in regards to the ice-point procedure. The temperature of the steam-point was found to be 348.07 K with a value of uncertainty of 0.0005 K. The known steam-point of water is 373 K. The experimental temperature was found to be approximately 24.93 K lower than the theoretical temperature. In an effort to establish a more accurate steam-point reading, a more enclosed system could potentially be employed for use in the steam pressure portion of the procedure. The experiment utilized an open system that was able to exchange heat in the form of the steam that escaped from around the bulb being utilized to read the pressure. Proposal of a better fitting bulb, longer duration spent reading the steam pressure, or longer period of cooldown for the bulb in between readings for ice pressure and steam pressure could ideally yield data producing calculated results aligning with the theoretical data. Conclusion The experimental objective to find the temperature of the two fixed points, ice and steam point, was successful. The calculated temperature of the ice point of water was off by a value that could be attributed to uncertainty, while the steam point was off by a temperature value within 30 K of the expected temperature. The gas thermometer apparatus was designed with gas laws in mind. The calculations used in this experiment are all derived from equations that represent these laws mathematically. Through the pressures obtained, an almost exact value for the ice point of water was found. The demonstrated functionality of a gas thermometer setup such as the one used in this experiment effectively create a system that would prove useful in industrial settings or continuation research laboratories. Improvements could be made in the steam collection aspect of the apparatus used. A more enclosed system for measuring the pressure of the steam could be utilized in the form of a tighter fitting bulb. Time and space allowing, the steam point having a separate gas thermometer apparatus could yield undisturbed and more accurate results without the necessity of switching a bulb pressure reader from an ice bath to a hot source in a short timeframe.
References 1. Garland, C. W.; Nibler, J. W.; Shoemaker, D. P. Experiments in Physical Chemistry ; McGraw-Hill Higher Education, 2009. 2. Harvey, A. H.; McLinden, M. O.; and Tew, W. L. Thermodynamic Analysis and Experimental Study of the Effect of Atmospheric Pressure on the Ice Point . https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=910516 (accessed 2024-01-22). 3. Moldover, M.R.; Tew, W.L.; Yoon, H.W. Advances in thermometry . Nat Phys. 2016 Jan;12:7-11. doi: 10.1038/nphys3618. Epub 2016 Jan 7. PMID: 27182278; PMCID: PMC4865254. Appendix Bulb Volume (V): Bulb diameter: 32 mm External bulb radius (r external ): 32 mm 2 = 16 mm Interior bulb radius (r): 16 mm 2 mm = 14 mm (volume of hemispheres) + (volume of cylinder) = total bulb volume (V) ( ( 4 3 π r 3 )+ ( π r 2 h ) = ¿ Propagation of Error for V: 0.05 2 + 0.05 2 = ± 0.07 mm Dead Space Volume (v): Dead space 1 : r = 6 mm, l = 40 mm, v 1 = π r 2 l = π ( 6 2 ) ( 40 ) = 4524 mm 3 = 45 cm 3 Dead space 2 : r = 1.5 mm, l = 120 mm, v 2 = 848 mm 3 = 8.5 cm 3 Dead space 3 : r = 1.5 mm, l = 150 mm, v 3 = 1060 mm 3 = 11 cm 3 Dead space 4 : l = 520 mm, v = ( 21 2 π ) 2 π ( 520 ) = 18249 mm 3 = 182 cm 3 Total volume of dead space (v): 247 cm 3
Propagation of Error for v: 0.05 2 + 0.05 2 + 0.05 2 + 0.05 2 = ± 0.1 mm Room Pressure (p r ): -287.7 Torr-(-733.3 Torr) (first & third zero) = 449.1 Torr Instrument Error for p r : 0.01 Torr [Trial 1] Measured Pressure of Ice Point (p 0 ): 313.2 Torr ( 733.7 Torr ) = 420.5 Torr Instrument Error for p 0 : 0.01 Torr [Trial 1] Measured Pressure of Steam Point: 197.0 Torr ( 733.7 Torr ) = 536.7 Torr Average Ice-Point Pressure (p 0 ): 420.5 Torr + 420.5 Torr + 419.2 Torr 3 = 420.1 Torr Average Steam-Point Pressure: 536.7 Torr + 535.8 Torr + 533.7 Torr 3 = 535.4 Torr [Trials 1 & 2] Ice-Point Temperature Approximation: T = 273.15 p 0 p = 273.15 420.1 Torr ( 420.5 Torr ) = 273.4 K Molar Volume of Bulb ( ~ V ): ~ V RT 0 p 0 = ( 62.36 L Torr K 1 mol 1 ) ( 273.1 K ) 420.1 Torr = 40.54 L mol 1 Propagation of Error for ~ V : σ ~ V = | 40.54 L mol 1 | ( 0.005 420.1 Torr ) 2 = 0.0005 ~ V = 40.54 L mol 1 ± 0.0005 L mol 1 [Trials 1 & 2] Ice-Point Temperature (T 0 ): B = T, 0 C = 11.8 for He 1 = 0.0118 L*mol -1 A A 0 = 1 + p p 0 p r v V + 3 t 1 ~ V ( B B 0 )= 1 + 420.5 Torr 420.1 Torr 4491.1 Torr ( 0.0247 L 0.048 L ) ¿ T = 273.15 p 0 A A 0 p = 273.15 420.1 Torr ( 0.9997 ) ( 420.5 Torr ) = 273.3 K Propagation of Error for p [Trials 1 & 2]: ( 0.05 420.5 ) 2 +( 0.05 420.1 ) 2 + ¿¿ Propagation of Error for p [Trial 3]: ( 0.05 4 19 . 2 ) 2 +( 0.05 420.1 ) 2 + ¿¿ [Trial 1] Steam-Point Temperature: B = T, 100 C = 11.4 for He 1 = 0.0114 L*mol -1 A A 0 = 1 + p p 0 p r v V + 3 t 1 ~ V ( B B 0 )= 1 + 536.7 Torr 420.1 Torr 4491.1 Torr ( 0.0247 L 0.048 L ) ¿ T = 273.15 p 0 A A 0 p = 273.15 420.1 Torr ( 0.9998 ) ( 536.7 Torr ) = 348.9 K
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Propagation of Error for p [Trial 1]: ( 0.05 536.7 ) 2 +( 0.05 420.1 ) 2 + ¿¿ Propagation of Error for p [Trial 2]: ( 0.05 535.8 ) 2 +( 0.05 420.1 ) 2 + ¿¿ Propagation of Error for p [Trial 3]: ( 0.05 533.7 ) 2 +( 0.05 420.1 ) 2 + ¿¿