Chapter 15 Problems Solving

CHAPTER 14- Practice Exercise Dr. PAHLAVAN______

Chemical Equilibrium

Problem #1. Write the equilibrium-constant expression (Kc and/or Kp) for the following reactions:

(a) H2 (g) + I2 (g ) « 2HI (g) (b) 2Cl2 (g) + 2H2O (g) « 4HCl (g)+ O2 (g)

Problem #2. How is the equilibrium-constant expression (Kc) for the reaction: 2NO (g) « N2 (g) + O2 (g); Kc=0.145; related to the following reaction?

(a) N2 (g) + O2 (g) « 2NO (g) K1=....………

(b) 4NO (g) « 2N2 (g) + 2O2 (g) K2=....……...

(d) 1/2 N2 (g) + 1/2 O2 (g) « NO (g) K4=....………

Problem #3. Given Kc or Kp for the following reactions, what is the value of Kp or Kc?

(a) I2 (g) + Cl2 (g) « 2ICl (g); Kc = 2.0 x105 at 25 oC

(b) N2O4 (g) « 2NO2 (g) ; Kc = 0.90 at 120 oC

Problem #4. Iodine molecules react reversibly with iodide ions to produce trioxide ions

I2 (aq) + I- (aq) ↔ I3 - (aq)

If a solution is prepared with the concentration of I2 and I- equal to 1.000 × 10-3 M before reaction

and if concentration of I2 changes to 6.61 × 10-4 at equilibrium, what is the equilibrium constant for

the reaction?

Problem # 5 A container contains an equilibrium mixture of H2 (g), I2 (g) , and HI (g) at 721 K. The

concentration of each substance present at equilibrium is 1.843x10-3 M , 1.843x10-3 M,

and 1.310x10-2 M, respectively. Calculate the values of Kc and Kp for the reaction :

H2 (g) + I2 (g) « 2HI (g)

Problem #6. A 2.0L container contains an equilibrium of 2.8x10-2 mole NO (g), 4.0x10-2 mole Br2 (g), and

2.0x10-2 mole NOBr (g) at 25 oC. Calculate Kc and Kp at 25 oC.

2NO (g) + Br2 (g) « 2NOBr (g)

Problem #7. A container initially holds 1.00 atm of NO2 (g) and 2.00 atm of NO (g). At equilibrium that

stablished is; 2NO2 (g) « 2NO (g) + O2 (g) ; all of the species are gases, Kp is 6.76x10-5. What is the equilibrium partial pressure of O2 (g)?

Problem # 8. The reaction: CO (g) + H 2O (g) ↔ CO2 (g) + H 2 (g) , has Kc = 4.1 at 500 ° C. Suppose you place

0.060 mol of CO and 0.060 mol of H 2O (g) in a 0.50 liter reaction vessel. The mixture is then

heated to 500 ° C. What are the concentration of the reactants and products when the system reaches

equilibrium?

Problem #9. A 1.00 L container initially contains 0.476 mol of SO3(g) at 1105 K. What is the Kc for the

reaction: if 50.0 percent of SO3 (g) has decomposed at equilibrium?

2SO3 (g) « 2SO2 (g) + O2 (g)

Problem #10. A 1.00 L container holds 0.015 mol of H2 (g) and 0.020 mol of I2 (g) at 721 K. What are the

concentrations(pressures) of H2 (g), I2 (g), and HI (g) after the system achieved a state of

equilibrium? The value of Kc is 50.0 for reaction: H2 (g) + I2 (g) « 2HI (g)

Problem #11. For the equation: C (s) + CO2 (g) « 2CO (g); the value of Kp is 167.5 at 1000 oC. If a 5.00 L

container initially contains 2.99 atm pressure of CO2 (g) at 1000 oC, what are partial pressure of CO2 (g)

and CO (g) at equilibrium?

Problrm 12. The value of Kc for reaction: H2 (g) + I2 (g) « 2HI (g); is 50.5. In what direction the reaction

proceed if the initial concentratios are as follows?

(a) [H2] = 0.015 M , [I2] = 0.012 M , [HI] = 0.024 M

(b) [H2] = 0.030 M , [I2] = 0.060 M , [HI] = 0.15 M

Problem #13. At 2000 ° C, the equilibrium constant for the reaction: N2 (g) + O2 (g) ßà 2NO (g) ,

is 4.1 × 10-4 . Find the concentration of NO (g) in a mixture of NO (g), N2 (g) and O2 (g).

In which at equilibrium [N2] = 0.036 mol L-1 and [O2 ] = 0.089 mol L-1

Problem #14. What changes in the equilibrium composition of the reaction: N2 (g) + O2 (g) « 2NO (g)

will occur at constant temperature if :

(a) the pressure (or concentration) of N2 (g) is increased? ______

(b) the pressure (or concentration) of NO (g) is increased? ______

(d) the total volume of the system is increased?

(e) add a catalyst? (f) decrease the concentration of O2 (g)?

Problem #15. What changes in the equilibrium composition of the reaction; 2CO (g) + O2 (g) « 2CO2 (g)

(exothermic) occur if:

(a) the concentration of O2 (g) increased? ______(b) the pressure of the system increased? ______

(e) cooling the reaction? ______