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Lab 12 Vapor Pressure and Enthalpy of Vaporization of Water Purpose: The Purpose of this experiment is to determine the enthalpy of vaporization of water (ΔH vap ) using the Clausis-Clapeyron Equation in respects to vapor pressure measurements of water at a number of temperatures. Data Analysis I: Air Pressure vs. Temperature Table 1: Effect of Temperature (°C) on Air Pressure (Torr) Temperature (ºC) Pressure (Torr) Total Air Pressure(Torr) a 40.5 8.5 768.5 38.5 5.5 765.5 36.5 2.0 762.0 34.5 -1.6 758.4 32.5 -5.3 754.7 30.5 -8.4 751.6 28.5 -12.5 747.5 a All Total Air Pressure (Torr) values were determined using the atmospheric pressure of 760 mmHg or 760 Torr. Figure 1:
25 27 29 31 33 35 37 39 41 43 735 740 745 750 755 760 765 770 775 f(x) = 1.75x + 697.88 R² = 1 Figure 1: Effect of Temperature (ºC) on Air Pressure (Torr) Temperature (°C) Air Pressure (Torr) Data Analysis II: lnP (vapor) vs. 1/Temp Table 2: Vapor Pressure of Water versus Temperature Temp. (°C) P(sensor) (Torr) P(total) (Torr) P(air) (Torr) P(vapor) (Torr) Temperature (K) 1/Temp (K -1 ) lnP(vapor) 39.70 48.89 808.89 767.43 41.46 312.85 0.0032 3.72 37.99 43.75 803.75 764.43 39.32 311.14 0.0032 3.67 35.73 37.27 797.27 760.47 36.80 308.88 0.0032 3.61 33.98 28.68 788.68 757.40 31.27 307.13 0.0033 3.44 32.07 22.70 782.70 754.06 28.64 305.22 0.0033 3.35 Figure 2:
0 0 0 0 0 0 0 0 0 0 0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 f(x) = - 4788.9x + 19.06 R² = 0.96 Figure 2: Vapor Pressure of Water 1/T (K-1) ln(P) (P in Torr) Calculations: Calculating ΔHvap Equation: y =− 4788.9 + 19.057 m = ∆ Hvap R m =− 4788.9 R = 8.314 J mol 1 K 1 ( 8.314 E 3 kj mol 1 K 1 ) -ΔHvap = x
-4788.9 ¿ ∆ Hvap 8.314E-3 kj mol 1 K 1 = 39.8149146 1 = 39.8149146 kj / mol Formulas: Clausis-Clapeyron Equation: ln P =− ( ∆Hvap R )( 1 T ) + C
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