Thursday, September 15, 2011

Exercise (6.1 Chemical Equilibrium)

1. Write the Kc or Kp if applicable, for the following reversible reactions at equilibrium:
    (a) PCl3 (g) + Cl2 (g) PCl5 (g)
    (b) HF (aq) + H2O (l) ↔ H3O+ (aq) + F- (aq)
    (c) 2 NO (g) + O2 (g) ↔ 2 NO2 (g)
    (d) N2 (g) + 3H2 (g) 2 NH3 (g)
    (e) NH4Cl (s) NH3 (g) + HCI (g)
    (f) CaCO3 (s) CaO (s) + CO2 (g)
    (g) H2O (l) + SO3 (g) H2SO4 (aq)

2. Calculate Kp for the following reactions:
    (a) CO (g) + H2O (g) CO2 (g) + H2 (g),      Kc = 4.05 at 500oC
    (b) 2CO (g) + O2 (g) 2CO2 (g),      Kc = 2.24 x 1022 at 1273oC

3. Calculate Kc for the following reactions:
    (a) 2 NO2 (g) N2O4 (g),      Kp = 6.5 x 10-2 at 100oC
    (b) 2 SO3 (g) 2 SO2 (g) + O2 (g),      Kp = 1.8 x 10-5 at 350oC

4. For the ammonia–formation reaction,
        N2 (g) + 3 H2 (g) 2 NH3 (g)      Kc = 2.4x10-3 at 1000 K
    Calculate the Kc for the following balanced equations at the same temperature.
    (a) 1/3 N2 (g) + H2 (g) 2/3NH3 (g)
    (b) NH3 (g)  ½N2 (g) + 3/2H2 (g)

5. For the following reaction at 60oC:
        H2S (g) + I2 (s) 2 HI (g) + S (s)
    the partial pressure of PHI = 3.65x10-3 atm and PH2S = 0.996 atm at equilibrium. Calculate Kp.

6. An equal amount of hydrogen and iodine are injected into a 1.50 L flask at a fixed temperature.
        H2 (g) + I2 (g) 2 HI (g)
    At equilibrium, it is found that the flask contains 1.80 mol of H2, 1.80 mol of I2 and 0.520 mol of HI. Calculate Kc.

7. 0.200 mol of hydrogen halide is injected into a 2.00 L flask at a fixed temperature.
        2 HI (g) H2 (g) + I2 (g)
    If [HI] = 0.078 M at equilibrium, calculate Kc.    

8. At 25°C, 0.0560 mol of O2 and 0.020 mol N2O are placed in a 1.00 L vessel and allowed to react according to the following equation:
        2 N2O (g) + 3 O2 (g) 4 NO2 (g)
   When the system reached equilibrium, the concentration of NO2 was found to be 0.020 mol L-1.
   (a) Calculate the concentration of N2O and O2 at equilibrium.
   (b) Calculate the equilibrium constant, Kc for the reaction.

9. At 25°C, Kp = 7.13 for the following reaction:
        2 NO2 (g)  N2O4 (g)
   If the partial pressure of NO2 in a container is 0.15 atm at equilibrium, calculate the equilibrium partial pressure of N2O4 in the mixture.

10. The equilibrium constant Kp for the following reaction is 158 at 1000K:
         2 NO2 (g) 2 NO (g) + O2 (g)
      Calculate the PO2 at equilibrium if PNO2 = 0.400 atm and PNO = 0.270 atm at equilibrium.

11. At 440°C, the equilibrium constant Kc = 49.5 for the following reaction:
        H2 (g) + I2 (g)  2 HI (g)
      If 0.200 mol of H2 and 0.20 mol of I2 are placed into a 10.0 L vessel and allowed to react at this temperature, calculate the concentration of each substance at equilibrium.

12. The equilibrium constant, Kc = 0.00465 for the following reaction at 25oC:
        N2O4 (g) 2 NO2 (g)
      If 0.67 M of N2O4 is injected into a vessel at the beginning of the reaction, calculate the equilibrium concentration of each substance at the same temperature.

13. 500 mol of ICl was placed in a 5.00 L flask and allowed to decompose at a high temperature:
        2 ICl (g) I2 (g) + Cl2 (g)       Kc = 0.110
Calculate the concentration of I2, Cl2 and ICl at equilibrium.         
        
14. A 1.000 L flask is filled with 1.000 mol of H2 and 2.000 mol of I2 at 448oC.  
        H2 (g) + I2 (g) 2 HI (g)       Kc = 50.5 at 448oC
     Calculate the partial pressure of H2, I2 and HI at equilibrium.

15. At 600 K, Kc for the following reaction is 1.7 x 108,
        2 SO2 (g) + O2 (g) 2 SO3 (g)
     (a) Calculate the partial pressure of SO2 (g) at equilibrium, if PSO3 = 300 atm and PO2 = 100 atm at equilibrium.
     (b) If a mixture of 0.0040 mol of SO2 (g) and 0.0028 mol of O2 (g) is placed in a 1.0 L container and the temperature is increased to 1000 K, 0.0020 mol of SO3 (g) is present at equilibrium. Calculate Kc and PSO2 at equilibrium for this reaction at 1000 K.

16. 0.4 mol of phosgene, COCl2 in a 2.0 L vessel decomposes into CO and Cl2 at 200oC. At equilibrium, it is found that 15% of phosgene had been decomposed. Determine the equilibrium constant, Kp for this reaction at 200oC.

17. At 250oC and 1 atm, the equilibrium constant, Kp for the dissociation of N2O4 to form NO2 is 9.18 x 10-2. Calculate the degree of dissociation of N2O4 under these conditions.

18. At 375°C, the initial concentration of N2, H2 and NH3 are 0.0711 M, 9.17 x 10-3 M and 1.83 x 10-4 M respectively.
        3 H2 (g) + N2 (g) 2 NH3 (g)
     If the equilibrium constant, Kc for the reaction is 1.2 at this temperature, decide whether the system is at equilibrium. If it is not, predict in which direction the reaction will proceed to reach equilibrium.

19. At 425oC, Kp = 4.18 x 10-9 for the reaction
        2 HBr (g) H2 (g) + Br2 (g)
     In one experiment, 0.20 atm of HBr (g), 0.010 atm of H2 (g), and 0.010 atm of Br2 (g) are introduced into a container. Is the system at equilibrium? If not, in which direction will it proceed to reach equilibrium?

20. The water–gas shift reaction plays a central role in the chemical methods for obtaining cleaner fuels from coal:
        CO (g) + H2O (g) CO2 (g) + H2 (g)
      In a given temperature, Kp = 2.7. If 0.13 mol of CO, 0.56 mol of H2O, 0.62 mol of CO2, and 0.43 mol of H2 are introduced into a 2.0 L flask, in which direction must the reaction proceed to reach equilibrium?

Answer
2. (a) 4.05
    (b) 1.77 x 1020
3. (a) 1.99
    (b) 3.52 x 10-7
4. (a) 0.134
    (b) 20.41
5. 1.34 x 10-5
6. 0.0836
7. 0.02
8. (a) [N2O] = 0.01 M
         [O2] = 0.041 M
   (b) 23.2
9. 0.16 atm
10. 347 atm
11. [H2] = [I2] = 0.0044 M
      [HI] = 0.0312 M
12. [N2O4] = 0.643 M
      [NO2] = 0.055 M
13. [I2] = [Cl2] = 0.02 M
      [ICl] = 0.06 M
14. H2 = 3.85 atm
      I2 = 63.01 atm
      HI = 110.64 atm
15. (a) 0.016 atm
      (b) Kc = 555.6
          0.164 atm
16. 0.20
17. 0.15
18. →
19. ←
20. ←

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