PS3.1. In the boxes below diagram the specific system as viewed at the particulate level in the space provided. Be sure to clearly label each of the substances in your diagram. (NOTE: Figures 1.2 and 5.1 in your textbook depicts particulate level diagrams of matter.)
A sample of NH3 at 25 °C
A sample of iron at 25 °C
A sample of nitrogen and carbon dioxide at 25 °C
PS3.2. Describe, in terms of a particulate level view, what happens as heat is added to a sample of a pure substance initially in the solid phase until the sample is completely vaporized. Use some or all of the terms like atom, molecules, particles, collisions, kinetic energy, speed, velocity, heat, temperature, intermolecular attractive forces, solid, liquid, gas.
PS3.3. Write a chemical equation describing the condensation process for N2 and a chemical equation describing the freezing process for N2. For each process discuss the change in enthalpy and entropy that occurs. For each process describe the conditions (in terms of temperature) that support a thermodynamically favorable change, and the conditions that do not support a thermodynamically favorable change.
PS3.4a. Define the term equilibrium vapor pressure.
b) Use a vapor-pressure table (check the Database link on the class web site) to look up and record below, the equilibrium vapor pressure of a sample of water at 87 °C and at 72 °C.
c) Consider two closed containers each partially filled with liquid water one at 87 °C and the other at 72 °C. Can the pressure of water vapor in the gas phase in either container ever exceed the equilibrium vapor pressure at the particular temperature? Explain why or why not.
PS3.5. A sample of water in the vapor phase (no liquid present) in a flask of constant volume exerts a pressure of 450 mm Hg at 98 °C. The flask is slowly cooled.
a). Assuming no condensation, use the Ideal Gas Law to calculate the pressure of the vapor at 87 °C; at 72 °C.
b) Will condensation occur at 87 °C; 72 °C? Explain.
c) On the basis of your answers in a) and b), predict the pressure exerted by the water vapor in the flask at 87 °C; at 72 °C.
PS3.6. Consider the following data for ammonia
Temperature ( °C)
Vapor Pressure (mmHg)
-37
572.47
-58
142.02
-38
538.74
-82
19.83
-35
645.42
-64
90.58
a) Use graphing software (Microsoft Excel) to plot ln(vp) versus T-1 (K-1) for ammonia and use your graph to determine the slope of the best line through the data. (If you are not familiar with Excel checkout the last few minutes in Friday, January 26th podcast.) The heat of vaporization of a liquid can be obtained from such a plot. The relation is given as,
slope = - H°vap/8.314 J mol-1K-1
Calculate the enthalpy of vaporization for ammonia.
b) Using the graph, determine the temperature (°C) of a sample of ammonia when the vapor pressure is 16.46 mmHg.
c) Using the graph, determine the vapor pressure (mmHg) of a sample of ammonia at -78 °C.
PS3.7. The normal boiling point of methanol is 65.0 °C and its H°vap = 37.4 kJ mol-1. Draw a complete Lewis structure for methanol and calculate the temperature at which methanol has a vapor pressure of 180.08 mmHg.
PS3.8. Using the data from PS3.7. calculate the vapor pressure of methanol when the temperature is 272 K.
PS3.9. Calculate the H°vap for an unknown liquid if its vapor pressure at 300 K is 140.8 mmHg and at 314 K its vapor pressure is 274.95 mmHg