Suggested Homework Set 2

BCH 341 – ASU ONLINE – iCourse – Spring 2018

J.P. Allen, BioPhysical Chemistry, Wiley-Blackwell, 2008. (free PDF version for ASU students)

Chapter 3: problems 5, 10, 13, 14, 15 & 17.

Chapter 4: problems 3, 8, 13, 16 & 18.

Additional Problems

2-1A: Calculate the change in energy for the process of taking an ice cube (typical ice cube is 1 in3) out of your freezer at -20°C and heating at atmospheric pressure to a final state of steam at 120°C.  It is very useful to look at this process from several thermodynamic perspectives.  Hence, it is suggested that you not only look at the various types of energy change that occurs in this common physical change process, but you also look at the change in entropy.  

2-2A: Consider the decomposition of solid magnesium carbonate to form solid magnesium oxide and gaseous carbon dioxide.  Calculate the temperature at which the decomposition is thermodynamically favorable under standard pressure conditions.

2-3A: How much ethane would you need to combust to heat a kilogram of water from room temperature to boiling?  (B) What about you switch and use propane.  Does it require more, less or the same amount?  (‘How much’ is a bit vague.  However, this is often exactly how people would speak or ask this type of question.  As chemists, the number of moles would be the most useful answer to the question ‘how much’ of a specific chemical compound.  However, this often isn’t the most practical for non-scientists.  The most useful for the general public is probably the volume that would be required from a standard propane/butane/natural gas tank.)

2-4A: A quanitity of 0.55 moles of an ideal gas initially at room temperature is expanded from 1.0 to 5.0 liters.  If this expansion is done slowing such that it is reversible and isothermal, what can you say about the change in energy of the system? (B) Determine as much as you can about this system thermodynamically.  So, for example, calculate the following: work (w), heat (q), the change in internal energy (ΔU), the change in enthalpy (ΔH), the change in entropy (ΔS) and the change in Gibbs free energy (ΔG).  Really, this part of the question and part (A) are asking for the same thing! All of these ‘thermodynamic’ quantities are energies (except entropy, which is only a T multiplication away from being an energy).

2-5A: 80 ml of water at room temperature is mixed with 160 ml of hot water (measured to be 176 F).  Calculate the change in entropy (ΔS) for the system (the entire system being all the mixed water).

2-6A: The reaction of carbon monoxide with water is a very important process and is generally called the water-gas shift reaction (WGSR).  At room temperature, is this reaction thermodynamically favorable? i.e., is it spontaneous? (B) What is the effect of temperature on the WGSR?

2-7A: Is the hydrogenation of ethylene a spontaneous reaction (thermodynamically favorable) at 100°C?

2.8A: At standard temperature and pressure (STP), 280 milliliters (ml) of an unknown gas has a weight of 200 milligrams (mg).  The gas was ignited and shown experimentally to be very combustible.  Provide an educated guess for what this ‘unknown’ gas could potentially be? and what experiment you would propose to provide further proof of the chemical composition of this unknown gas.


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