Thermodynamics

In this experiment you will learn about two ways to study phase transitions by analysis of iodine and of binary solutions.

Preparation

Binary Solutions

  1. What are the goals of this experiment? What does it have in common with the second experiment?
  2. Theory:
    1. Write down Raoult's law, and explain each term.
    2. Explain the reasons for positive and negative deviations from Raoult's law, and give examples for solutions that express each deviation.
  3. Experimental setup:
    1. Draw the experimental setup, and explain the purpose of each chamber.
    2. Why does it have to be in a vacuum?
    3. What are the factors that can cause the pressure measured to be higher or lower than expected?
  4. Expected results:
    1. Find the expected vapor pressures for these substances: methanol, ethanol, acetone, benzene, and toluene.
    2. What behavior would you expect with the following solutions relative to that of an ideal solution: acetone and ethanol, acetone and benzene, and toluene and benzene. Explain your expectations.

Iodine Sublimation

  1. What are the goals of this experiment?
  2. Theory:
    1. The absorption of light is described by the Beer-Lambert law: I = I0e−σnx. Explain the meaning of each component in this equation. Why do we use this form and not I = I010−εcx?
    2. During the experiment you will use Planck's equation to calculate the temperature of the lamp. Write down the necessary equations, and explain each term.
    3. Explain these terms:
      1. Black body. What is the black body in our system?
      2. Dark current. What are the possible sources for a dark current in our experiment?
      3. In the last part of this experiment, you will calculate the enthalpy of iodine sublimation. What equations will you use, and what assumptions do you have to make?
  3. Experimental setup:
    1. What are the advantages and disadvantages of each parameter of the program that can be adjusted (integration period, average period and Boxcar smoothing)?
    2. What is the purpose of the optic fiber? What is it made of? How does it work?
    3. What are the purposes of the diffraction grating and the CCD? How does each influence the signal?
    4. How does the thermocouple work? Where exactly is the reference temperature measured in the device?
    5. What is the boiling temperature of iodine (see the Recommended Literature section)? Explain how it is possible to measure the absorption of iodine at temperatures that are lower than the boiling temperature.
    6. Why is the maximum temperature of the iodine sample limited to 70-80 °C.
    7. We have two lamps in our experiment. What are their purposes?
  4. Expected results:
    1. What is the supplier's value for the lamp temperature? What color does it correspond to?
    2. Find the entire spectrum of iodine for comparison with your results. At which wavelengths does iodine gas absorb light?
    3. How can you find the maximum absorption wavelength from the iodine spectrum?
    4. Find a value in the literature for ΔH of iodine sublimation.