Klotz & Treichel: Chemical Equilibrium

Chapter 16: Principles of Reactivity: Chemical Equilibrium-p 786: 2, 3, 6, 8, 10, 12, 14, 16, 18, 22, 30, 36, 40, 42, 50, 52, 56, 58, 60, 70

Answers at the bottom

16.2. Decide if each of the following statements is true or false. If false, change the wording to make the statement true.

  1. The magnetude of trhe equilibrium constant is always independent of temperature.
  2. When two chemical equations are added to give a net equation, the equilibrium constant for the net euqation is the product of the equilibrium constants of the summed equations.
  3. The equilibrium constant for a reaction has the same value as K for its reverse.
  4. Only the concentration of CO2 appears in the equilibrium constant expression for the reaction
  5. For the reaction the value of K is the same whether the amount of CO2 is expressed in moles per liter or as gas pressure.


16.3. Neither PbCl2 nor PbF2 is appreciably soluble in water. If solid PbCl2 and solid
PbF2 are placed in equal amounts of water in separate beakers, in which beaker is
the concentration of Pb2+ greater? Equilibrium constants for these solids
dissolving in water are

PbCl2(s) Pb2+(aq) + 2 Cl-(aq) K = 1.7 x 10-5

PbF2(s) Pb2+(aq) + 2 F-(aq) K = 3.7 x 10-8

16.6 The decomposition of calcium carbonate

CaCO3(s) CaO(s) + CO2(g)

is an endothermic process. Using Le Chatelier's principle, explain how increasing
the temperature affects the equilibrium. If more CaCO3 is added to the flask in
which this equilibrium exists, how is the equilibrium affected? What if some
additional CO2 is placed in the flask?


16.8 Write equilibrium constant expressions for the following reactions. For gases, use
Either pressures or concentrations.

  1. 3 O2(g) 2 O3(g)
  2. SiH4(g) + 2 O2(g) SiO2(g) + 2 H2O(g)
  3. Ni(s) + 4 O(g) Ni(CO)4(g)
  4. (NH4)2CO3(s) 2 NH3(g) + CO2(g) + H2O(g)
  5. BaSO4(s) Ba2+(aq) SO42-(aq)


16.10. How is the equilibrium constant Kc for the reaction of hydrazine and chlorine
trifluoride

N2H4(g) + 4/3 ClF3(g) 4 HF(g) + N2(g) + 2/3 Cl2(g)

related to K'c for the reaction written in the following way

3 N2H4(g) + 4 ClF3(g) 12 HF(g) + 3 N2(g) + 2 Cl2(g)

  1. Kc = K'c
  2. Kc = 1/K'c
  3. 3Kc = K'c
  4. (Kc)3 = K'c
  5. Kc = (K'c)3



16.11. Calculate Kc for the reaction

SnO2(s) + 2 CO(g) Sn(s) 2 CO2(g)

Given the following information:

SnO2(s) + 2 H2(g) Sn(s) + 2 H2O(g), Kc = 8.12

H2(g) + CO2(g) CO(g) + H2O(g), Kc = 0.771


16.14. The equilibrium constant Kc for the reaction

H2(g) + Cl2(g) 2 HCl(g)

At 500 K is 4.8 x 1010. Calculate Kc for

  1. 1/2 H2(g) + 1/2 Cl2(g) HCl(g)
  2. HCl(g) 1/2 H2(g) + 1/2 Cl2(g)


16.16. Kc = 5.6 x 10-12 at 500 K for the reaction

I2(g) 2 I(g)

A mixture kept at 500 K contains I2 at a concentration of 0.020 mol/L and I at a
Concentration of 2.0 x 10-8 mol/L. Which way must the reaction go to reach
equilibrium?


16.18. The reaction

2 NO2(g) N2O4(g)

has an equilibrium constant, Kc, of 170 at 25ºC. If analysis of the system shows that
2.0 x 10-3 mol of NO2 is present in a 10.-L flask long with 1.5 x 10-3 mol of N2O4,
is the system at equilibrium? If it is not at equilibrium, does the concentration of NO2
increase or decrease as the system proceeds to equilibrium?


16.22. The reaction

C(s) + CO2(g) 2 CO(g)

occurs at high temperatures. At 700ºC, a 2.0-L flask contains 0.10 mol of CO, 0.20
mol of CO2, and 0.40 mol of C at equilibrium.

  1. Calculate Kc for the reaction at 700ºC.
  2. Calculate Kc for the reaction, also at 700ºC, if the amounts at equilibrium in the 2.0-L flask are 0.10 mol of CO, 0.20 mol of CO2, and 0.80 mol of C.

16.30. Cyclohexane, C6H12 (a hydrocarbon), can isomerize, or change, into methylcyclopentane, a compound of the same formula but with a different molecular
structure

C6H12(g) C5H9CH3(g)

cyclohexane methylcyclopene

The equilibrium constant has been estimtaed to be 0.12 at 25ºC. If you had originally
Placed 0.045 mol of cyclohexane in a 2.8-L flask, what are the concentrations of cyclohexane and methylcyclopentane when equilibrium is established?


16.36. At 450ºC, 3.60 mol of ammonia is placed in a 2.00-L vessel and allowed to decompose
to the elements.

2 NH3(g) N2(g) + 3 H2(g)

If the experimental value of Kc is 6.3 for this reaction at this temperature, calculate the
Equilibrium concentration of each reagent.


16.40. The oxidation of NO to NO2

2 NO(g) + O2(g) 2 NO2(g)

is exothermic. Predict the effect of the following changes on the position of the
equilibrium; that is, state which way the equilibrium will shift (left, right, or no change)
when each of the following changes is made:

  1. Adding more O2(g)
  2. Adding more NO2(g)
  3. Increasing the volume of the reaction flask
  4. Lowering the temperature


16.42. The value of Kc for the decomposition of ammonium hydrogen sulfide is 1.8 x 10-4 at
25ºC.

NH4HS(s) NH3(g) + H2S(g)

  1. When the pure salt decomposes in a flask, what are the equilibrium concentrations
    of NH3 and H2S?
  2. If NH4HS is placed in a flask already containing 0.020 mol/L of NH3 and then
    the system is allowed to come to equilibrium, what are the equilibrium concentrations
    of NH3 and H2S?


16.50. One mole of Br2 is placed in a 1.00-L flask and heated to 1756 K, a temperature at
which the halogen dissociates to atoms.

Br2(g) 2 Br(g)

If Br2 is 1.0% dissociated at this temperature, calculate Kc.

16.52. Equal numbers of moles of H2 gas and I2 vapor are mixed in a flask and heated to
700ºC. The initial concentration of each gas is 0.0088 mol/L, nd 78.6% of the I2 is
consumed when equilibrium is achieved according to the reaction

H2(g) + I2(g) 2 HI(g)

Calculate Kc for this reaction.


16.58. At 250ºC Kp = 0.039 for the reaction

2 NOCl(g) 2 NO(g) + Cl2(g)

Calculate Kc for the reaction.

16.60. At 2300 K the equilibrium constant for the formation of NO(g) is Kc = 1.7 x 10-3.

N2(g) + O2(g) 2 NO(g)

  1. If analysis shows that the concentrations of N2 and O2 are both 0.25M, and that
    of NO is 0.0042 M, is the system at equilibrium?
  2. If the system is not at equilibrium, in which direction does the reaction proceed?
  3. When the system is at equilibrium, what are the equilibrium concentrations?

16.70 1-Butene can change, or isomerize, to trans-2-butene in the gas phase.


click for larger view

An equilibrium plot for this reaction is given in the figure.

  1. What is the value of K for the equilibrium?
  2. If for the reaction is -11.5 kJ/mol. does the value of K increase or decrease as the temperature increases?
  3. Use the equilibrium plot to find the equilibrium concentrations of reactant and product when 1.20 mol/L of 1-butene is added to an equilibrium mixture, whose concentration of 1-butene is 0.60 mol/L.
  4. Consider the transformation of 1-butene to cis-2-butene. The value of Kc for this reaction is 8.84. Construct an equilibrium plot similar to the one for 1-butene and trans-2-butene. Compare the slope of the line in this polt with the slope of the line for the 1-butene/trans-2-butene equilibrium.
  5. What is the equilibrium constant for the transformation of trans-2-butene to cis-2-butene?


answers

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