7387788-P-CHEM-Lab-6

7387788-P-CHEM-Lab-6 - Tompall Toone Nathaly Murillo Aaron...

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Tompall Toone Nathaly Murillo Aaron Reinicker Physical Chemistry I Chem 445-021 Experiment 6 Vapor Pressure of a Pure Liquid Abstract In this experiment the vapor pressure of methanol was measured by means of a vacuumed isoteniscope in a stirred water bath. The heat of vaporization as calculated by the Clausius-Clapeyron equation was ∆Hvap = 33.104 + 0.968 kJ/mol, which is somewhat close to the literature value of ∆Hvap =35.21 kJ/mol. Using the Antoine equation the heat of vaporization was calculated to be ∆Hvap = 50.085 + 0.351 kJ/mol. The Antoine Equation provides a better fit for the experimental data since most of the residuals are 0 or extremely close to the experimental data when compared to the Clausius-Clapeyron equation. Two trials were performed. The second trial appeared to be more accurate since the values of its Antoine coefficients ( A = 8.754, B = 2025.15, C = 280.549) were closer to the literature values (A = 8.07240, B = 1574.990, C = 238.870) . The Antoine coefficients for trial 1 were calculated as: ( A = 10.75, B=3926.05, C = 434.57).
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Introduction In this experiment, the vapor pressure of methanol was measured. Vapor pressure of a pure compound is an intensive property that is independent of the amounts of the two phases (gas and liquid) as long as both are present. It is defined as the pressure of a system in which the gas of a substance is in dynamic equilibrium with its liquid form. Since vapor pressure strongly increases as a function of temperature and slightly increases as a function of applied pressure, it was necessary to record the vapor pressure. The vapor pressure of the system was measured using a MKS Baratron pressure gauge in which it increased strongly as a function of increasing temperature. The following equation relating the variation of vapor pressure with temperature was used to analyze the results: (1) The above equation is known as the Clausius-Clayeron equation and was used under the assumption that the heat of vaporization is independent of temperature. In equation 1, P represents the vapor pressure of the liquid, T represents the temperature in Kelvin, and ΔH vap stands for the molar heat of vaporization for methanol. Equation 1 will give an accurate fit to vapor pressure data over a wide range of temperatures, as long as the temperature is well below the critical temperature. This will cause compensating errors in the analysis, and therefore a more accurate equation is required to consider the variation of vapor pressure with temperature. Hence the following equation, the Antoine equation, was used to give a more elaborate method for finding vapor pressure as a function of temperature: (2)
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A, B, and C in the Antoine equation are empirical constants obtained from a fit to the data. Procedure
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This note was uploaded on 09/23/2009 for the course CHEM 120 taught by Professor Johnmichael during the Spring '09 term at Tennessee Martin.

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7387788-P-CHEM-Lab-6 - Tompall Toone Nathaly Murillo Aaron...

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