Chem321:Problem Set 2

Problem Set #2

Due February 22nd, 2008. Please type up your answers in Microsoft Word, Word Perfect, OpenOffice Writer or RTF file format, and email to me before midnight on the evening of Friday, June 10th. Do not post your answers on the wiki.

1. Explain briefly the meaning of the following terms: The Two Cultures (from CP Snow), the science of ecology, exergy, closed system, scientific hypothesis, Law of Constant Composition.
2. (~100 words) What is sustainability science, and how does it differ from environmental science?
3. (~300 words) Explain the difference between science and technology. Other than providing the foundation for the design of new environmental technologies, what are some ways in which pure science can be used to aid the environment.
4. Inside a perfectly closed system – a sealed tank of water, a large moving rock is brought to a halt. What happened to its kinetic energy (energy of motion)?
5. A change from solid to liquid, or liquid to gas, is always accompanied by an increase in entropy. Also, any chemical reaction that INCREASES the number of molecules INCREASES the entropy, while one that DECREASES the number of molecules DECREASES the entropy. Which of the following changes involve an increase in entropy?

a) Molten iron from a furnace freezes into solid ingots.

b) Natural gas burns in a home heater: 2C₄H₁₀ + 13O₂ ---> 8CO₂ + 10H₂O c) A piece of iron rusts: 4Fe + 3O₂ ---> 2Fe₂O₃ d) A puddle of water evaporates on a sunny day e) Polyethylene is made from ethylene, by combining many small molecules into a few large ones. n C₂H₄ ---> (C₂H₄)n where n is a large number (>10,000). f) Acid rain leaches aluminum ions out of the soil and into solution in the groundwater. 6) When one mole of methanol (wood alcohol) boils at 338 K, it requires the input of 35,300 J of heat, but there is an increase of entropy of 127 J. What is the overall change in the Gibbs Free Energy? 7) Design a hypothesis to explain the following observations in the "Acme scenario" below, then explain what experiments you might perform in order to test your hypothesis. You do not need to know any chemistry to solve the problem, just a logical approach that uses the evidence. (Note: It's very loosely based on a real incident)

Acme Chemical Company scenario requiring a hypothesis.

There has been an explosion in the reactor V388, while running the DMBTFE process. No one was hurt, thankfully, but you want to know why so that you can prevent it happening again.

(a) The CTV process involves the following steps:

a. Add sodium hydride (a solid used as a base, it reacts violently with water and many acidic materials, but it is stable to dry air and oxygen). The correct amount of sodium hydride would be delivered in plastic bags shortly before this step was carried out.

b. Add toluene (a flammable, but otherwise stable liquid). This would be metered into the reactor directly from a storage tank.

c. Add trifluoroethanol (TFE, a weakly acidic liquid) slowly. This was added over several hours via a delivery funnel.

d. Add DMSO (a high-boiling liquid, non-flammable), using a drum pump (which is a small pump that delivers an exact amount of material from a metal drum of the DMSO into the reactor).

e. Add 2,4-dimethoxybenzyl bromide (a lachrymator, it tends to burns the skin and eyes), as a solution in DMSO.

f. Add water, and separate the two layers. The product (DMBTFE) goes into the toluene layer, which is then transferred to another reactor for further processing.

(b) The explosion occurred during step c, near the start of the addition of TFE.

(c) The same process had been successfully carried out on 142 batches prior to this, without any incident.

(d) The correct amount of sodium hydride was delivered, and all the bags were found to be empty.

(e) The correct amount of trifluoroethanol was measured out, and tests on the residual TFE indicated that it was dry..

(f) The water delivery line was physically disconnected when the explosion occurred, and there were no other ways in which water could get into the reactor. [Such safety precautions are common practice in the industry – the line would be reconnected when it was safe to add the water]

Questions

What is the most likely combination of chemicals that caused the explosion? Develop a hypthesis, consistent with the above information, that matches the observations. How could you see if it was true or not?