Vapor Pressure and Heat of Vaporization Introduction: ?Evaporation is the process of a liquid becoming vaporized. When a liquid is placed into a confined space some of the liquids will evaporate. Evaporation of the liquid depends on the strength of the intermolecular forces that are between liquid molecules. During the evaporation process of the liquid, new gas molecules exerts pressure in the sealed container, while some of the gas condenses back to the liquid state. ?If the temperature inside the container is kept constant, then the equilibrium at some point will be reached.
When the equilibrium is reached, the rate of condensation is equal to the rate of evaporation and the rate of vapor pressure will remain constant as long as the temperature in the sealed container does not change. ?The relationship between the vapor pressure of a liquid and temperature is described in the Clausius-Clayperon equation: lnP= ? Hvap / R (1/T)+C. where 1nP is the natural logarithm of the vapor pressure, ? Hvap is the change in heat vaporization, R is the universal gas constant, which is (8. 31 J/mol•K), T is the absolute, or Kelvin, temperature, and C is the constant that is not related to heat capacity.
Therefore, Clausius-Clayperon equation does not only describes how vapor pressure is affected by the temperature, but relates to the factors of heat vaporization of a liquid. ?The purpose of this experiment is to determine the relationship between the pressure and temperature of the volatile liquids. The pressure will be measured in a sealed vessel that contains different types of liquids such as methanol, ethanol and propanol. It will be measured several times at different temperatures. At the conclusion of this experiment, the heat of vaporization will be able to be calculated.
Materials: ?To be able to complete this lab procedure, the materials that are needed is a Vernier computer interface, a Vernier Gas Pressure Sensor, temperature probe, rubber stopper assembly, plastic tubing with two connectors, hot plate, ice, one twenty milliliter syringe, one 400 milliliter beaker, two 125 milliliter Erlenmeyer flasks, one 1 liter beaker, ethanol, methanol, and 1-propanol. Methods: ?The first step in performing this experiment is to obtain and wear goggles. The alcohols used in this experiment are flammable and poisonous.
The second step is to obtain the materials that are needed and set them up as accordingly. The third step is to use a hot plate to heat 200 milliliters of water in a 400 milliliter beaker. The fourth step is to prepare a room temperature water bath in a 1 liter beaker. The fifth step is to connect the Gas Pressure Sensor to channel one of the Vernier computer interface, then connect the Temperature Probe to channel two of the interface and then connect it to a computer. The sixth step is to use the clear tubing to connect the white stopper to the Gas Pressure Sensor.
The white stopper must be twisted snugly into the neck of the Erlenmeyer flask, to avoid losing any of the gas that will be produced when the liquid starts evaporating. The most important thing to do is to remember to close the valve on the white stopper. ?The seventh step is to draw in 3 milliliters of methanol into the 20 milliliter syringe that is part of the Gas Pressure Sensor accessories. Place the syringe onto the valve of the white stopper. The eighth step is to start the Logger Pro program and open the file “34 Vapor” from the Advanced Chemistry with Vernier folder. The ninth step is to click “collect” to begin collecting data.
The first measurement will be the pressure of the air in the flask and the room temperature. Place the Temperature Probe near the flask. When the pressure and temperature readings are stabilized, click “keep” to record the readings. The tenth step is to add methanol to the flask by opening the valve below the syringe, push down on the syringe to inject the 1-propanol and quickly close the valve. Afterwards, remove the syringe from the stopper and monitor the pressure and temperature readings. ?The eleventh step is to place the stoppered flask into the 1 liter beaker of room temperature water.
Place the Temperature Probe in the water bath and monitor the pressure and temperature readings. The twelfth step is to add a small amount of hot water to warm the water bath by only a few degrees. Stir the water with the temperature probe and monitor the pressure and temperature readings. For the thirteenth step, repeat step twelve until five trials are completed. Add hot water for each trial so the temperature of the water bath increases. After the fifth trail is recorded, open the valve to release the pressure in the flask and dispose of the alcohol as directed.
The fifteenth step is to end the data collection and record the pressure and temperature readings in the data table. When recording the data, record the pressure valve of the first data point as Pair for trials one and two and record the temperature for trial one. Record the pressure value of the second data point as Ptotal for trial two as well as the temperature. The remaining values are recorded as Ptotal for trial two as well as the appropriate temperature. The last and final step is to clean the work area. Data Table: Methanol Trial 1 Trial 2 Trial 3 Trail 4 Trail 5 Ptotal (mmHg) 103. 1 04. 5 105. 8 101. 9 Pair (mmHg) 101. 3 102. 4 103. 3 104. 4 105. 2 Pvap (mmHg) 0. 7 1. 2 1. 4 2. 7 Temperature (Celsius) 22. 6 25. 8 28. 3 31. 2 34. 0 Ethanol Trial 1 Trial 2 Trial 3 Trail 4 Trail 5 Ptotal (mmHg) 106. 3 94. 7 98. 9 112. 9 Pair (mmHg) 100. 8 100. 8 92. 78 96. 0 103. 4 Pvap (mmHg) 5. 4 1. 92 2. 9 9. 5 Temperature (Celsius) 23. 9 24. 0 0. 3 9. 9 31. 7 Propanol Trial 1 Trial 2 Trial 3 Trail 4 Trail 5 Ptotal (mmHg) 101. 7 104. 9 106. 1 108. 3 Pair (mmHg) 100. 4 101. 1 102. 2 103. 1 104. 0 Pvap (mmHg) 0. 6 2. 7 3. 0 4. 3 Temperature (Celsius) 23. 8 23. 7 0. 2 6. 5 29. 1 Discussion At the end of this experiment, the results we obtained varied because of the different temperatures and pressures that we observed. During the evaporation process of the liquid, gas molecules exerts pressure in the sealed container, while some of the gas condenses back to the liquid state. If the temperature inside the container is kept constant, then the equilibrium was reached. When the equilibrium is reached, the rate of condensation is equal to the rate of evaporation and the rate of vapor pressure will remain constant as long as the temperature in the sealed container does not change.