Chemical Equilibrium


The following problems are taken from T. L. Brown, H. E. Lemay, B. E. Bursten, & J. R. Burdge, Chemistry: The Central Science, Ninth Edition, Chapter 15. To see the solution to a problem or to return from the solution, click on the number of the problem.


12) The equilibrium constant for the reaction

       2NO(g) + Br2(g) 2NOBr(g)

       is Keq = 1.3 x 10-2 at 1000 K..

       (a) Calculate Keq for 2NOBr(g) 2NO(g) + Br2(g)

       (b) At this temperature does the equilibrium favor NO and Br2, or does it favor NOBr?


14) Consider the following equilibrium, for which Keq = 0.0752 at 480°C:

       2Cl2(g) + 2H2O(g) 4HCl(g) + O2(g)

      (a) What is the value of Keq for the reaction 4HCl(g) + O2(g) 2Cl2(g) + 2H2O(g)?

      (b) What is the value of Keq for the reaction Cl2(g) + H2O(g)2HCl(g) + 1/2O2(g)?

      (c) What is the value of Keq for the reaction 2HCl(g) + 1/2O2(g)Cl2(g) + H2O(g)?


22) Phosphorus trichloride gas and chlorine gas react to form phosphorus pentachloride gas:

      PCl3(g) + Cl2(g) PCl5(g)

      A gas vessel is charged with a mixture of PCl3(g) and Cl2(g), which is allowed to equilibrate at 450 K. At equilibrium the partial pressures of the three gases are PPCl3 = 0.124 atm, PCl2 = 0.157 atm, and PPCl5 = 0.130 atm.

      (a) What is the value of Keq at this temperature?

      (b) Does the equilibrium favor reactants or products?

24) A mixture of 1.374 g of H2 and 70.31 g of Br2 is heated in a 2.00-L vessel at 700 K. These substances react as follows:       

      H2(g) + Br2(g) 2HBr(g)

      At equilibrium the vessel is found to contain 0.566 g of H2.

      (a) Calculate the equilibrium partial pressures of H2, Br2, and HBr.

      (b) Calculate Keq.


32) At 900 K the following reaction has Keq = 0.345:

      2SO2(g) + O2(g)   2SO3(g)

      In an equilibrium mixture the partial pressures of SO2 and O2 are 0.165 atm and 0.755 atm, respectively. What is the equilibrium partial pressure of SO3 in the mixture?


38) At 21.8°C, Keq = 7.0 x 10-2 for the equilibrium

      NH4HS(s) NH3(g) + H2S(g)

      Calculate the equilibrium partial pressures of NH3 and H2S if a sample of solid NH4HS is placed in a closed vessel and decomposes until equilibrium is reached.    

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