CHM 1046

Test #2

Chang: Chapters 15 and 16

 

  1. In a 1.00 L flask 0.00882 moles of H2 and 0.00589 moles of I2 are combined and allowed to react at a temperature of 643° C. After the reaction comes to equilibrium 0.00572 moles of HI have been produced. What is Kc for the reaction

H2(g) + I2(g) ß à 2 HI(g)
      1.   1.81 b. 67.3 c. 0.630 d. 2.39 e. 7.18

 

  1. The following reaction was allowed to come to equilibrium at 427 K.

2 NO(g) + O2(g) ß à 2 NO2(g)
The equilibrium concentrations were analyzed and found to be:

                   

[O2] = 0.733 M

[NO2] = 0.907 M

[NO] = 0.818 M
The value of Kc is
 
      1. 1.68 b. 1.24 c. 1.40 d. 2.39 e. 0.418

  

  1. The equilibrium constant is Kc = 1.98 x 1012 for

    2.

    H2(g) + Br2 ß à 2 HBr(g)

    What is Kc for the reverse reaction

    HBr(g) ß à H2(g) + Br2(g)

    a.4.62 x 10-9 b. 2.16 x 10-10 c. 6.23 x 10-9 d. 149 e. 5.05 x 10-13

     

  2. For the equilibrium reaction below , the value of Kc = 1.06 x 10-16 at a certaintemperature. Which predominates at equilibrium?

CO2(g) + H2(g) ß à CO(g) + H2O(g)

  1. products greatly predominate
  2. products moderately predominate
  3. reactants greatly predominate
  4. reactants moderately predominate
  5. there are equal amounts of products and reactants

 

  1. The equilibrium constant for the following reaction at 708° C is 67.5. 

SO2(g) + NO2(g) ß à NO(g) + SO3(g)

To start the reaction 1.5 moles of both SO2 and NO2 were placed in a 1.0 L reactor. What is the concentration of NO after the reaction reaches equilibrium?  
      1. O.55 M b. 1.5 M c. 12 M d. 1.3 M e. 1.0 M

 

  1. The following reaction has Kc = 4.62 x 109

  CO(g) + Cl2(g) ß à COCl2(g)

At equilibrium [Cl2] = 0.236 M and [COCl2] = 0.330 M. What is the concentration of CO in moles/L?
  1. 3.03 x 10-10 b. 3.2 x 1022 c. 3.07 x 10-23 d. 5.54 x 10-12 e. 42

 

  1. 0.0423 moles of NO2 were placed in a 1.00 L flask and allowed to react. At

    2. equilibrium [O2] = 0.0188 M. What is the value of Kc?

    2 NO2(g) ß à 2 NO(g) + O2(g)

    a. 192 b. 25 c. 1.2 d. 14.6 e. 1.86 x 10-5

     

    The next several questions refer to the equation

    2 NOBr(g) ß à 2 NO(g) + Br2(g) D H° = -92 kJ

    In each question tell how the number of moles of Br2 at equilibrium is. affected by the change.

     

  2. Adding more moles of NO.

    3. a.. increase b. decrease c. no change

     

  3. Raising the temperature. 

        a. increase b. decrease c. no change

 

  1. Decreasing the volume.
  1. increase b. decrease c. no change

 

  1. Removing NOBr
  1. increase b. decrease c. no change

 

  1. Adding a catalyst
  1. increase b. decrease c. no change

 

  1. For which of these reactions is the position of equilibrium unaffected by changes in volume?

 

  1. Br2(g) + Cl2(g) ß à 2 BrCl(g)
  2. Br2(g) ß à 2 Br(g)
  3. 2 CH4(g) ß à C2H2(g) + 3 H2(g)
  4. HCl(g) + NH3(g) ß à NH4Cl(s)

 

  1. For the reaction  

C(s) + O2(g) ß à 2 CO(g) D H° = -221 kJ

Which of the following will cause an increase in Kc?

  1. a decrease in volume
  2. removing some O2
  3. adding a catalyst
  4. increasing the temperature
  5. decreasing the temperature

 

  1. For the reaction

N2(g) + 3 H2(g) ß à 2 NH3(g) Kc = 0.65

Starting with 2.0 mole of each reactant and product in a 1.0 L container, when this mixture comes to equilibrium

  1. the moles of ammonia will have increased
  2. the moles of ammonia will have decreased
  3. no change will have occurred

 

  1. Chemical equilibrium exists when
  1. reactants are completely changed to products
  2. there are equal amounts of reactants and products
  3. the rate at which reactants form products becomes zero
  4. the rate at which reactants form products is the same as the rate at which products form reactants

 
  1. When a system at equilibrium is disturbed by a decrease in pressure (increase in volume), the equilibrium will shift to the side with ______ moles of _______ in order to ________ the pressure.

 

  1. more, gas, increase
  2. more, solid, decrease
  3. fewer, gas, decrease
  4. fewer, gas, increase
  5. the same, gas, equalize

 

  1. HS- + HF ß à F- + H2S

In this reaction ______ acts as the Bronsted acid and ________ is its conjugate base.

a.HF, HS-

b.HF , H2S

c.HS-, F-

d.HS-, H2S

e. HF , F-

 

  1. In the above reaction ____ acts as the Bronsted base and _____ is its conjugate acid.

    2. a.HF, HS-

    b.HF , H2S

    c.HS-, F-

    d.HS-, H2S

    e. HF , F-

     

  2. If pH = 7, what is pOH?
  1. 10-11 b. 10-3 c. 7 d. 11 e. 3

 

  1. What is the [OH-] if pH = 12.64?
  1. 2.7 x 10-6 M b. 3.7 x 10-9 M c. 5.8 x 10-8 M d. 0.0443 M

 

  1. What is the [H3O+] if the pH = 7.24?

    2.  

    a. 4.6 x 10-6 M b. 2.2 x 10-9 M c. 5.34 M d. 5.8 x 10-8 M

     

  2. What is the pH if [H3O+] = 8.7 x 10-11 M?
  1. 5.29 b. 8.72 c. 6.51 d. 7.00 e. 10.06

 

  1. What is the pH if [OH-] = 1.0 x 10-6 M?
  1. 8.00 b. 6.00 c. 7.00 d. 2.55 e. 0.79

 

  1. What is the pH of an NaOH solution that has a concentration of 0.052 M?
  1. 0.98 b. 1.28 c. 13.02 d. 12.02 e. 12.72

 

  1. What is the [H3O+] of a 0.19 M solution of HCN? The Ka

= 4.0 x 10-10.
  1. 0.19 M b. 8.7 x 10-6 M c. 1.8 x 10-5 M d. 1.7 x 10-4 M

 

  1. What is the pH of a 0.66 M solution of NH3? (Kb = 1.8 x 10-5)
  1. 11.54 b. 2.46 c. 0.66 d. 13.82 e. 11.26

 

  1. A 0.50 M solution of HX was found to have a pH of 2.00. What is the Ka for this acid?

 

  1. 9.9 x 10-4 b. 2.0 x 10-4 c. 6.5 x 10-7 d. 1.9 x 10-2 e. 8.8 x 10-12

 

For the next several questions indicate whether the aqueous solution has a

  1. pH less than 7 b. pH greater than 7 c. pH about 7

 

  1. FeCl3(aq)
  1.  KCl(aq)
  1. NaF(aq)
  1. KNO3(aq) 
  1. Na3PO4(aq)

    2.   

  2. When Na2S undergoes hydrolysis the main products are

 

  1. Na+ and OH- b. H+ and HS- c. H+ and OH- d. OH- and HS-

 

  1. The strongest acid below is

 

HC2H3O2 + H2O ß à H3O+ + HC2H3O2-

Ka = 1.8 x 10-5

HCN + H2O ß à H3O+ + CN-

Ka = 4.0 x 10-10

HClO4 + H2O ß à H3O+ + ClO4-

Ka >> 1

 

  1. HC2H3O2 b. HCN c. HClO4 d. H3O+ e. H2O

 

  1. The strongest base below is
  1. C2H3O2- b. CN - c. ClO4 - d. H3O+ e. H2O

 

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