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vp_and_enthalpy

# vp_and_enthalpy - Vapor Pressure and Enthalpy of...

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Vapor Pressure and Enthalpy of Vaporization of Water Kyle Miller November 19, 2006 1 Purpose The purpose of this experiment is to calculate the enthalpy of vaporization of water by finding the vapor pressure of water over a range of temperatures. 2 Procedure In an inverted 10mL graduated cylinder, a sample of air is trapped. The cylinder is submerged in a 1L beaker of water. The distance between the surface of the water in the beaker to the top of the water in the cylinder is then measured and shall be denoted as h . The beaker is heated to 80 C and the volume of the air is measured. While stirring the water in the beaker to be sure of even heat distribution, let the water cool and record the volume of the gas every 5 C. After the temperature of the beaker reaches 50 C, the beaker is cooled to near 0 C by adding ice. The volume of air and the near-zero temperature is measured. 3 Data The following data were collected: P atmosphere = 747 . 81 mmHg h = 74 . 5 mm 1

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Table 1: Measured values T ( C) V (mL) 17 5.13 73.1 10.00 70 9.20 65 8.58 60 8.02 55 7.43 50 7.10 1.0 5.40 4 Calculations 0. T k is in K so it is T + 273. For example, 17 C + 273 = 290K. 1. To correct for inverted menisci, 0.20mL is subtracted from each volume reading. So, Cor- rected V = V - 0 . 20mL. For example, corrected V = 10 . 00mL - 0 . 20mL = 9 . 80mL 2. The pressure on the cylinder is P cylinder = P atmosphere + h · 1 . 00 13 . 6 mmHg. Substituting in the actual values, P cylinder = (747 . 81 + 74 . 5 13 . 6 )mmHg = 753mmHg 3. The number of moles of trapped gas is n air = P · V R · T where R = 62 . 4 mmHg
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vp_and_enthalpy - Vapor Pressure and Enthalpy of...

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