Equilibrium Constant Expression

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CHM 096

TUTORIAL 2 (Chemical Equilibrium)

Jan 2013

1.

Write the equilibrium constant expression, Kc, for each of the following reactions: a) b) c) d) e) f) 2NO(g) + O2(g) ⇄ 2NO2(g) The decomposition of solid potassium chlorate to solid potassium chloride and oxygen gas. 4HCl(g) + O2(g) ⇄ 2H2O(g) + 2Cl2(g) 2NO2(g) + 7H2(g) ⇄ 4H2O(l) + 2NH3(g) H2O(g) + C(s) ⇄ CO(g) + H2(g) The reduction of solid copper (II) oxide with hydrogen gas to produce copper metal and water at o 500 C. 2H2(g) + O2(g) ⇄ 2H2O(g) are 2.50, 1.35 x 10‒5 and 8.70 moles respectively in a 12-L flask. Calculate the equilibrium constant 7 Kc. (1.08 x 10 )

2.

The number of moles of H2, O2, and H2O present at equilibrium for the reaction:

3.

The equilibrium constant Kc for the reaction: 2HCl(g) ⇄ H2(g) + Cl2(g) is 0.0213 at 400 C. If 20.0 o moles of HCl(g) are heated at 400 C, what amounts of HCl(g), H2(g) and Cl2(g) would be present in the equilibrium mixture? (H2 = Cl2 = 2.26 moles; HCl = 15.48 moles) o

4.

The equilibrium constant Kc for the reaction: 2CO(g) + O2(g) ⇄ 2CO2(g) is 2.24 x 10 at 1273 C. Calculate the Kp for the reaction at the same temperature. 20 (1.76 x 10 ) 22 o

5.

A 2.50 mole sample of NOCl was placed in a 1.50-L container at 400 C. When equilibrium has established, it was found that 28% NOCl has dissociated according to the reaction: 2NOCl(g) ⇄ 2NO(g) + Cl2(g) Calculate the equilibrium constant Kc (0.0356)

o

6.

Consider the reaction: H2(g) + CO2(g) ⇄ H2O(g) + CO(g) 0.80 mole of H2 and 0.80 mole of CO2 are placed in a 5-dm container at 1650 C. At equilibrium, 0.25 mole of CO was found in the equilibrium mixture. Calculate the equilibrium constant K c. (0.2) 3 o

7.

For the reaction:

2NO2(g) ⇄ N2O4(g) , the value of Kc is 0.5 at 450 C.
o o

A 1-L container consists of 2.0 moles NO2 and 2.0 mole N2O4 450 C. Is the mixture at equilibrium? If not, in which direction must the reaction proceed to reach equilibrium? 8. Kc and Kc are the equilibrium constants for reactions I and II respectively. I. II. a) b) c) 9. 3H2(g) + N2(g) ⇄ 2NH3(g) ³/2 H2(g) + ½ N2(g) ⇄ NH3(g) ’ ’

Write the equilibrium constant expressions for Kc and for Kc . Derive a mathematical relationship ’ between Kc and Kc . A reaction vessel contains an equilibrium mixture of 0.11 M N 2(g), 1.91 M H2(g) and 0.25 M NH3(g) o at 500 C. Calculate the equilibrium constant, Kc for reaction I. (0.082) ’ Calculate also the equilibrium constant, Kc for reaction II. (0.29) 4 o

For the reaction: 2NO(g) + Cl2(g) ⇄ 2NOCl(g), Kp is 6.5 x 10 at 35 C. At equilibrium, the partial pressure PNO = 0.35 atm and PCl2 = 0.10 atm. Calculate the equilibrium partial pressure of NOCl. (28.2 atm)

10.

For the reaction: C(s) + 2H2(g) ⇄ CH4(g), Kp is 0.262 at 1000 C. At equilibrium, the partial pressure PH2 = 1.22 atm. Calculate the equilibrium partial pressure of CH4(g). (0.39 atm) o

11.

1.0 mole of PBr5 is added to a 1-dm container at 200 C and is allowed to attain equilibrium according to the reaction: PBr5(g) ⇄ PBr3(g) + Br2(g) The equilibrium mixture contains 0.61 mole of PBr5(g) a) b) Calculate the partial pressure of each of the components in the container. (PPBr5 = 23.7 atm; PPBr3 = 15.15 atm) Calculate the Kp for the reaction. (Kp = 9.68)

3

o

12.

Phosgene gas (COCl2) is a highly toxic chemical. 3.00 x 102 mol of the gas was placed in a 1.50-L container. It was heated to 800K. An equilibrium is established: COCl2 (g) ⇄ CO(g) + Cl2(g) The equilibrium pressure of CO was 0.497 atm. Calculate: a) b) the number of mol of CO in the equilibrium mixture. the equilibrium constant Kc and Kp.

(0.01135 mol, 4.60 x 103, 0.302)

13.

Consider the reversible system: 2NO(g) + Cl2(g) ⇄ 2NOCl(g) Predict the direction of equilibrium shift: a) b) if a small amount of Cl2(g) is introduced into the mixture at equilibrium. if the volume of the container is doubled. Predict the effect of decreasing temperature on the equilibrium system:...
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