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Key equations

  • Q = [ C ] x [ D ] y [ A ] m [ B ] n where m A + n B x C + y D
  • Q P = ( P C ) x ( P D ) y ( P A ) m ( P B ) n where m A + n B x C + y D
  • P = MRT
  • K P = K c ( RT ) Δ n

Chemistry end of chapter exercises

Explain why there may be an infinite number of values for the reaction quotient of a reaction at a given temperature but there can be only one value for the equilibrium constant at that temperature.

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Explain why an equilibrium between Br 2 ( l ) and Br 2 ( g ) would not be established if the container were not a closed vessel shown in [link] .

Equilibrium cannot be established between the liquid and the gas phase if the top is removed from the bottle because the system is not closed; one of the components of the equilibrium, the Br 2 vapor, would escape from the bottle until all liquid disappeared. Thus, more liquid would evaporate than can condense back from the gas phase to the liquid phase.

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If you observe the following reaction at equilibrium, is it possible to tell whether the reaction started with pure NO 2 or with pure N 2 O 4 ?
2 NO 2 ( g ) N 2 O 4 ( g )

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Among the solubility rules previously discussed is the statement: All chlorides are soluble except Hg 2 Cl 2 , AgCl, PbCl 2 , and CuCl.

(a) Write the expression for the equilibrium constant for the reaction represented by the equation AgCl ( s ) Ag + ( a q ) + Cl ( a q ) . Is K c >1,<1, or ≈ 1? Explain your answer.

(b) Write the expression for the equilibrium constant for the reaction represented by the equation Pb 2+ ( a q ) + 2 Cl ( a q ) PbCl 2 ( s ) . Is K c >1,<1, or ≈ 1? Explain your answer.

(a) K c = [Ag + ][Cl ]<1. AgCl is insoluble; thus, the concentrations of ions are much less than 1 M ; (b) K c = 1 [ Pb 2+ ] [ Cl ] 2 >1 because PbCl 2 is insoluble and formation of the solid will reduce the concentration of ions to a low level (<1 M ).

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Among the solubility rules previously discussed is the statement: Carbonates, phosphates, borates, and arsenates—except those of the ammonium ion and the alkali metals—are insoluble.

(a) Write the expression for the equilibrium constant for the reaction represented by the equation CaCO 3 ( s ) Ca 2+ ( a q ) + CO 3 ( a q ) . Is K c >1,<1, or ≈ 1? Explain your answer.

(b) Write the expression for the equilibrium constant for the reaction represented by the equation 3 Ba 2+ ( a q ) + 2 PO 4 3− ( a q ) Ba 3 ( PO 4 ) 2 ( s ) . Is K c >1,<1, or ≈ 1? Explain your answer.

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Benzene is one of the compounds used as octane enhancers in unleaded gasoline. It is manufactured by the catalytic conversion of acetylene to benzene: 3 C 2 H 2 ( g ) C 6 H 6 ( g ) . Which value of K c would make this reaction most useful commercially? K c ≈ 0.01, K c ≈ 1, or K c ≈ 10. Explain your answer.

Since K c = [ C 6 H 6 ] [ C 2 H 2 ] 3 , a value of K c ≈ 10 means that C 6 H 6 predominates over C 2 H 2 . In such a case, the reaction would be commercially feasible if the rate to equilibrium is suitable.

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Show that the complete chemical equation, the total ionic equation, and the net ionic equation for the reaction represented by the equation KI ( a q ) + I 2 ( a q ) KI 3 ( a q ) give the same expression for the reaction quotient. KI 3 is composed of the ions K + and I 3 .

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For a titration to be effective, the reaction must be rapid and the yield of the reaction must essentially be 100%. Is K c >1,<1, or ≈ 1 for a titration reaction?

K c >1

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Practice Key Terms 7

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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