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Alberta Chemistry 30

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Additional Review Questions

Unit 5

Unit 6

Unit 7

Unit 8

UNIT 7 Chemical Equilibrium Focusing on Acid-Base Systems

Chapter 15 Equilibrium Systems

Chapter 15 Additional Review Questions

1. What are two ways to describe the relative amounts of reactants and products present in a chemical reaction at equilibrium?

2. Butane lighters can be dangerous. They can stay lit, melt, and then react explosively. They may leak and then cause a fire. They can be made child resistant but not child proof. The phase equilibrium is hard to maintain at all conditions. Liquid butane in lighters escapes in the gas phase when the lighter is opened. Butane lighters do not work well outdoors in very cold weather.

•  Write an expression for the phase equilibrium of butane in a lighter.
•  Use the phase equilibrium expression to explain why and to predict whether the pressure (concentration) of butane gas in the lighter is related to the quantity of liquid butane present.
 

Chapter 16 Equilibrium in Acid-Base Systems

Chapter 16 Additional Review Questions

1. Using the acid-base table, determine the K b for nitrite ions.

2. Consider an equilibrium reaction that produces a valuable and useful chemical. The percent reaction, under industrial, process conditions, is 74 %. If the product, at equilibrium, is present as 200 L of 0.22 mol/L solution, calculate the initial chemical amount of limiting reagent used.

Use this information to answer questions 3 to 9.

The petroleum and petrochemical industries have a chronic problem with the fact that all fossil fuels contain some sulfur atoms. If not removed, these sulfur atoms react upon burning to form SO 2 (g). Sulfur dioxide is irritating to lung tissue, highly corrosive, and a major contributor to air pollution and acid rain. As well, sulfur atom impurities may damage fuel injection and anti-pollution systems in modern internal combustion engines if not removed from gasoline and diesel fuels. In a refinery or upgrader, the sulfur is first removed from fossil fuel feedstock by cracking and/or hydrogenation, resulting in the sulfur reacting to produce (highly toxic) H 2 S(g). Standard industry technology to remove this toxic gas from the petrochemical gas stream mixtures involves the use of an amine scrubber unit, in a two-step process that depends on an acid-base equilibrium for its operation. For simplicity, assume that an amine scrubber contains a 25% solution of diethanolamine, (C 2 H 4 OH) 2 NH(aq), which approximates the actual solution used in the various tar sands plants in Alberta.

3. Draw a Lewis formula for diethanolamine, and identify the specific part of its structure that makes it a good proton attractor; that is, a Brønsted - Lowry base. (Hint: This molecule may be considered an ammonia molecule, with two of its hydrogen atoms replaced by ethanol side groups.)

4. All the other gases mixed with H 2 S(g) in a refinery process gas stream will be hydrocarbons. State both of the obvious reasons why hydrocarbon gases will not be "absorbed" by an aqueous solution of a Brønsted - Lowry base such as diethanolamine.

5. The exothermic reaction of hydrogen sulfide gas with aqueous diethanolamine involves a single proton transfer.Write the Brønsted - Lowry equilibrium reaction equation for this reaction.

6. In the first industrial process step, the mixed gases (light organic molecules and hydrogen sulfide) are injected at very high pressure into the reaction vessel containing the amine solution. Use Le Châtelier's principle to predict how the acid - base reaction equilibrium is shifted, and what effect this shift has on the original gas mixture.

7. In the second process step, the solution is moved to a new vessel where the pressure is lowered, but the temperature is greatly increased. Predict how this change shifts the acid - base reaction equilibrium, and what effect it will have on the solution.

8. Once sulfur atoms have been removed from a petrochemical mixture in this way, a further process is required. Hydrogen sulfide gas is difficult to store and handle, as well as being flammable, corrosive, explosive, and extremely toxic. By law, it must be converted on site to a safer substance. This conversion is accomplished with the Claus reactions: a two-step industrial process involving careful stoichiometric control of reacting amounts. Research this process on the Internet or in a text reference under "Claus Converter," and write the quantitative reaction equations that occur in these reaction vessels. Explain how the concept of limiting a reagent in a quantitative reaction is applied to make this process work.

9. Work within a group to research, assemble and present a summary of the operation of an industrial amine "scrubber" system. Emphasize the role of chemical equilibrium in this reaction system. Include information on applications of this process throughout Alberta . Your presentation should include use of the best features of any available word processing or slideshow software.