Thermodynamics Homework Problem Set

This problem set was developed by S.E. Van Bramer for Chemistry 145 at Widener University.

  1. Nitrogen Oxides are very important species in atmospheric chemistry. They are critical for a number of reactions that contribute to photochemical smog. The major anthropogenic (man made) source of NO is from the following reaction:

    N2 + O2 <--> 2 NO

    In this problem you will study the temperature dependence of this reaction to learn how the emission of NO may be reduced. Answer the following questions (assume that H is constant at each temperature):

    1. What is [delta] Hrxn, [delta] Srxn, [delta] Grxn, and K (We will assume that [delta] Hrxn and [delta] Srxn do not change with temperature. This is not strictly true and in more advanced courses you will learn how to account for these changes.) at:

      1. 25 C
      2. 1000 C
      3. 2000 C
      4. 3000 C

    2. The atmospheric pressure of N2 is 0.80 atm and O2 is 0.20 atm. Determine the equilibrium pressure of NO at each of the above temperatures.

    3. At high temperatures the above reaction is fast enough that the system can reach equilibrium. When exhaust gases leave a combustion chamber (an automobile, truck, boiler, or power plant) the air quickly cools. At the lower temperature the reaction is much slower so the system does not return to equilibrium. Would lowering the combustion temperature from 3000 C to 2000 C have any effect on the NO emission?

    4. Dr Madigoski and I recently purchased an instrument to determine the concentration of NO and NO2 with funds provided by a grant from the National Science Foundation. Based upon the Gibbs free energy, which of the following reactions is a feasible mechanism for converting NO into NO2 at ambient temperatures?

      1. 2 NO + O2 <--> 2 NO2
      2. NO + O3 <--> NO2 + O2
      3. NO + NO3 <--> 2 NO2
      4. CH3OO + NO <--> NO2 + CH3O

  2. Calculate [delta] G at 20C for the reaction H2 + I2 <--> 2 HI. Starting with 1.0 atm H2 and 1.0 atm I2. What is [delta] G when:

    1. 0.1% has reacted
    2. 1% has reacted
    3. 10% has reacted
    4. 50% has reacted
    5. 90% has reacted
    6. 99% has reacted
    7. 99.9% has reacted

  3. Using values from your textbook calculate [delta]So and [delta]Go for the following reactions:
    1. N2 (g) + 2 O2 (g) --> 2 NO2 (g)
    2. CO2 (g) + H2 (g) --> CO + H2O (g)
    3. 4 Al (s) + 3 O2 (g) --> 2 Al2O3 (s)
    4. 4 CO2 (g) + 2 H2O (g) --> 2 C2H2 (g) + 5 O2 (g)

Please send comments or suggestions to

Scott Van Bramer
Department of Chemistry
Widener University
Chester, PA 19013

© copyright 1996, S.E. Van Bramer
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Last Updated: Saturday, May 18, 1996