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General Chemistry Principles, Patterns, and Applications, 2011

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13. Figure 14.27 "Hydrogenation of Ethylene on a Heterogeneous Catalyst" illustrates the mechanism for the<br />

reduction of ethylene on a platinum surface to produce ethane. Industrially important silanes are synthesized<br />

using a related mechanism <strong>and</strong> are used to increase adhesion between layers of glass fiber <strong>and</strong> between<br />

layers of silicone rubber. Predict the products of the following reactions:<br />

14. In catalysis, if a molecule forms strong bonds to the catalyst, then the catalyst may<br />

become poisoned. Experiments on various catalysts showed the following results:<br />

a. Fe, Ru, <strong>and</strong> Os form weak bonds with N 2 ; however, O 2 , alkynes, alkenes, CO, H 2 , <strong>and</strong><br />

CO 2 interact more strongly.<br />

b. CO 2 <strong>and</strong> H 2 form weak bonds with a Co or Ni surface.<br />

c. Rh, Pd, Ir, <strong>and</strong> Pt form weak bonds with H 2 but do not bond with CO 2 .<br />

d. Cu, Ag, <strong>and</strong> Au form weak bonds with CO <strong>and</strong> ethylene.<br />

e. Explain why Fe was chosen as a catalyst to convert nitrogen <strong>and</strong> hydrogen to ammonia.<br />

Why is Fe more suitable than Ru or Os?<br />

f. Because alkenes generally interact more strongly with metal surfaces than does H 2 , what<br />

catalyst would you choose for hydrogenation of an alkene such as ethylene?<br />

g. Although platinum is used in catalytic converters for automobile exhaust, it was not found<br />

to be a particularly effective catalyst for the reaction of H 2 with a mixture of carbon<br />

monoxide <strong>and</strong> carbon dioxide to produce methane. Why?<br />

h. If you were interested in developing a catalyst to reversibly bind ethylene, which of the<br />

catalysts listed here would you choose?<br />

14. Nonstoichiometric metal oxides can be effective catalysts for oxidation–reduction reactions. One such<br />

catalyst is Ni 1−x O, found to be effective for converting CO to CO 2 when oxygen is present. Why is it so<br />

effective?<br />

15. The chemical reactions in an organism can be controlled by regulating the activity of certain enzymes.<br />

Efficient regulation results in an enzyme being active only when it is needed. For example, if a cell needed<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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