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General Chemistry Principles, Patterns, and Applications, 2011

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3. ♦ Phosphorus pentachloride, an important reagent in organic chemistry for converting alcohols to alkyl<br />

chlorides (ROH → RCl), is hydrolyzed in water to form phosphoric acid <strong>and</strong> hydrogen chloride. In the gaseous<br />

state, however, PCl 5 can decompose at 250°C according to PCl5 g<br />

which K = 0.0420.<br />

( ) PCl3( g)<br />

+ Cl2 g<br />

( ), for<br />

a. Are products or reactants favored in the decomposition of PCl 5 (g)?<br />

b. If a 2.00 L flask containing 104.1 g PCl 5 is heated to 250°C, what is the equilibrium<br />

concentration of each species in this reaction?<br />

c. What effect would an increase in pressure have on the equilibrium position? Why?<br />

d. If a 1.00 × 10 3 L vessel containing 2.00 × 10 3 kg of PCl 3 with a constant chlorine pressure of<br />

2.00 atm is allowed to reach equilibrium, how many kilograms of PCl 5 are produced? What<br />

is the percent yield of PCl 5 ?<br />

4. ♦ Carbon disulfide (CS 2 ) is used in the manufacture of rayon <strong>and</strong> in electronic vacuum tubes. However,<br />

extreme caution must be used when h<strong>and</strong>ling CS 2 in its gaseous state because it is extremely toxic <strong>and</strong> can<br />

cause fatal convulsions. Chronic toxicity is marked by psychic disturbances <strong>and</strong> tremors. CS 2 is used to<br />

synthesize H 2 S at elevated T via the following reaction:<br />

a.<br />

CS2 g<br />

( ) + 4H2( g) CH 4( g) + 2H2S( g) K = 3.3´104<br />

If the equilibrium concentration of methane in this reaction is 2.5 × 10 −2 M <strong>and</strong> the initial<br />

concentration of each reactant is 0.1635 M, what is the concentration of H 2 S at equilibrium?<br />

b. Exposure to CS 2 concentrations greater than 300 ppm for several hours can start to<br />

produce adverse effects. After working for several hours in a laboratory that contains large<br />

quantities of CS 2 , you notice that the fume hoods were off <strong>and</strong> there was not enough<br />

ventilation to remove any CS 2 vapor. Given the equilibrium CS2( l)<br />

CS2( g),<br />

where T =<br />

20°C <strong>and</strong> K p = 0.391, determine whether you are in any danger.<br />

5. ♦ Chloral hydrate, a sedative commonly referred to as “knockout drops,” is in equilibrium with<br />

trichloroacetaldehyde in highly concentrated aqueous solutions:<br />

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

Saylor.org<br />

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