Physical chemistry experiment Dr. Wenfeng Han jackhanwf@hotmail.com

Physical chemistry experiment It’s important to understand the theory and procedure before experiment. Following the instruction and recording all the data . Prepare the report on your own. Don’t Copy others! After experiment, show your data to me and leave the lab upon approval. Two students as a team. I will collect your reports during next experiment. Experiment handouts and report: http://www.hxsyzx.zjut.edu.cn

Experiments 4 Vapor Pressure of a Pure Liquid

Experimental objectives 1. Relationship between vapor pressure and temperature 2. Run a vacuum apparatus.

1. Vapor pressure Lnp vs. 1/T ----straight line its slope =？ the equilibrium gas phase A(l) ↔ A(g) Clapeyron-Clausius equation Lnp vs. 1/T ----straight line its slope =？

Relationship of p –T Control the pressure-----Vacuum system(pump) Vacuum pump Manometer Buffer Two-way valve Temperature (heater, thermometer) Power source Stirrer Output voltage of power source Sample (pure water)

2. Apparatus Feeding Manometer Condenser Two-way valve Equilibrium chamber Thermometer Two-way valve Liquid riser Feeding Vacuum pump Magnetic bar Heater Buffer Power source Magnetic stirrer

Experimental procedure Turn on the manometer Leak test Vacuum the system to around -45 kPa and wait for 5 min. If the change of reading is less than 0.25 kPa. c) Switch on the cooling water for the condenser. d) Switch off Valve 13，and turn on the pump, turn on Valve 13 slowly vacuuming the system to -42 to -43 kPa. .

Experimental procedure e) Tune the stirrer to a suitable stirring rate (Do not stir too vigorously). f) Adjust the output voltage of power source (There is a black mark for proper output volt). g) After water boils, adjust the output voltage to get a condensation rate in condenser 7 of 6~10 drops/min. When the temperature (Thermometer 4) maintain stable, record the temperature and the corresponding vacuum pressure (manometer 14). h) Increase the pressure in the system by 3-5 mmHg (around 6 kPa) by allowing a small amount of air to enter through tap B slowly. As the pressure in the system increases, boiling will stop. It is now necessary to increase the heating to start the boiling again. Record the new boiling point and the corresponding pressure.

Data analysis The pressure of the system P = Atmospheric pressure – Reading of manometer The atmospheric pressure is read directly on a Fortin Barometer. Viscosity determination Compare your determined viscosity with literature value and calculate the experimental error.

Calculate the enthalpy of vaporization of water Plot ln P versus 1/T. The unit of temperature should be in Kelvin!!! Calculate the enthalpy of vaporization of water The standard evaporation heat of water: