Vapor Pressure and Heat of Vaporization

Lab Report: Vapor Pressure and Heat of Vaporization Introduction The main objectives in this experiment is to measure the pressure inside a sealed vessel containing a volatile liquid over a range of temperatures, determine the relationship between the pressure and temperature of the volatile liquid, and calculating the heat of vaporization of the liquid. When a liquid is placed in a tightly sealed container, a portion of the liquid will evaporate, which will create gas molecules that apply pressure in the container. When there is a constant temperature inside the container, equilibrium is reached. At equilibrium, the rate of condensation is equal to the rate of evaporation and evaporation takes place at any point. The relationship between the vapor pressure of a liquid and temperature is used in the Clausius-Clayperon equation, ln P= -ΔHvap/R*(1/T)+C. Where ln P is the natural logarithm of the vapor pressure, ΔHvap is the heat of vaporization, R is the universal gas constant (8.31 J/mol*K), T is the absolute or Kelvin temperature, and C is constant. The Clausius-Clayperon equation relates to these factors to calculate the heat of vaporization of the liquid. Heat of vaporization is the amount of energy required to create the evaporation of one mole of liquid at constant pressure. In this experiment, we will measure the pressure in the vessel that contains the volatile liquid at several different temperatures and by analyzing the measurements; we can calculate the heat of vaporization of the liquid. This experiment relates to the concepts being studied, because we are determining the heat of vaporization over a range of different temperatures that are introduce by volatile liquid, which is sealed tightly in a container that contains pressure. As well as, examining the relationship between pressure and temperature of the volatile liquid. Procedure and Data Sheet Submitted as the carbon-less copy of the pre-lab outline (see attached) and data sheet. Materials Used LabQuest 20 mL syringe LabQuest App Two 125 mL Erlenmeyer flasks Vernier Gas Pressure Sensor Ethanol, CH3CH2OH Temperature Probe 400 mL beaker Rubber stopper assembly 1 liter beaker plastic tubing with two connectors Hot plate Results and Discussions The purpose of this experiment is to measure the pressure inside a sealed vessel containing a volatile liquid over different temperatures, examine the relationship between the pressure of the volatile liquid and temperature, and calculating the heat of vaporization of the liquid. We noticed that by adding hot water to the ethanol of the flask for each trial that is where we get varies temperature and pressure readings. Our measurement in this experiment for the pressure total (kPa) and the temperature (degrees Celsius) for trial 1 is 100.80 kPa and 27.8°C. Trial 2 is 104.02 kPa and 31.1°C. Trial 3 is 105.65 kPa and 33.7°C. Trial 4 is 107.94 kPa and 37.1°C. Lastly, Trial 5 is 108.61 kPa and 38.1°C. To calculate the pressure of the air for trials 15 are determined by using the gas law relationship equation, P1/T1=P2/T2. P1 is the initial of the pressure of the air and T1 is the initial temperature in Kelvin and P1 and T1 is used for all of the trials, the only that does change is the P2 and T2. So P2 is the unknown and T2 is the temperature of each of the trials in Kelvin. The pressure of the air for trial 1 is 98.27 kPa, trial 2 is 99.34 kPa, trial 3 is 100.20 kPa, trial 4 is 101.30 kPa, and trial 5 is 101.63 kPa. The next step is to calculate the vapor pressure, which for each trial you subtract the pressure of the air from the total pressure. The vapor pressure for trial 1 is 2.53 kPa, trial 2 is 4.68 kPa, trial 3 is 5.45 kPa, trial 4 is 6.63 kPa, and trial 5 is 6.97 kPa. The graph of the vapor pressure and the temperature of the volatile liquid does follow the expected trend of the effect of temperature on vapor pressure because it is a direct relationship. The second graph is the reciprocal of Kelvin temperature (1/T) and the logarithm of Pvap, lnPvap, which it is use to calculate the ΔHvap from the slope of the linear regression. I used the Clausius-Clayperon equation, ln P= -ΔHvap/R*(1/T)+C to calculate the heat of vaporization. To calculate the percent error, you use the equation, actual-theoretical/actual*100. So the percent error is 35.05%. Any discrepancy identified in this experiment is if the graphs are not a direct relationship or that follows the expected trend of the effect of temperature on vapor pressure. Sample Calculations Trial 1: (98.27 / 27.8 + 273) = (P2 / 27.8 + 273) o P2 = 98.27 kPa Pvap = 100.80 – 98.27 = 2.53 kPa Trial 2: (98.27 / 27.8 + 271) = (P2 / 31.1 + 273) o P2 = 99.34 kPa Pvap = 104.02 – 99.34 = 4.68 Kpa Trial 3: (98.27 / 27.8 + 273) = (P2 / (31.1 + 273) o P2 = 100.197 kPa Pvap = 125.65 – 100.197 = 5.453 kPa Trail 4: (98.27 / 27.3 + 273) = (P2 / 37.1 + 273) o P2 = 101.30 kPa Pvap = 107.94 – 101.30 = 6.631 kPa Trail 5: (98.27 / 27.8 + 273) = (P2 / 38.1 + 273) o P2 = 101.63 kPa Pvap = 108.61 – 101.63 = 6.97 kPa Conclusion This experiment was conducted to determine the heat of vaporization by examining the relationship between the vapor pressure and different temperatures of ethanol, which the graph was found to be a direct relationship. The result for heat of vaporization is 27.486 by simply multiplying the slope of the line by R, gas constant and the percent error is 35.05%. Overall, this experiment introduces a specific volume of a volatile liquid into a closed vessel, which in this case was ethanol, and to measure the pressure in the vessel at several different temperatures by adding hot water from the beaker, and from analyzing the measurements to calculate the heat of vaporization. Pvap vs. Celsius Temperature kPa) 12 10 8 The effect of vapor pressure and temperature Logarithm of Pvap (lnPvap) 2.5 2 f(x) = − 3307.71867612293 x + 12.8963607565012 1.5 1 0.5 0 0.0032 0.00325 0.0033 Kelvin Tmeprature (1/T) 0.00335 0.0034