Equilibrium Practice Problems

1.  Write the equilibrium expression for each of the following reactions:

N2 (g) + 3 H2 (g) « 2 NH3 (g)

I2 (s) + Cl2 (g) « 2 ICl (g)

NO2 (g) « NO (g) + ½ O2 (g)

2. The dissociation of acetic acid, CH3COOH, has an equilibrium constant at

25°C of 1.8 x 10-5. The reaction is CH3COOH (aq) « CH3COO- (aq) + H+ (aq)

If the equilibrium concentration of CH3COOH is 0.46 moles in 0.500 L of

water and that of CH3COO- is 8.1 x 10-3 moles in the same 0.500 L,

calculate [H+] for the reaction.

3.  Indicate the effect of a catalyst, pressure, temperature and concentration on each of the following on:

catalyst pressure temperature concentration

a.  speed

4.  Calculate Kp for the following equilibrium at 250°C if K = 0.042.

PCl5 (g) « PCl3 (g) + Cl2 (g)

5.  The reaction 2 NO (g) « N2 (g) + O2 (g) has a value of

K= 2400 at 2000 K. If 0.61 g of NO are put in a previously empty 3.00 L

vessel, calculate the equilibrium concentrations of NO, N2, and O2.

7.  Using the same reaction as in #6, calculate the equilibrium concentrations of NO, N2, and O2 if the initial concentrations of each species are:

[NO] = 0 M, [N2] = 0.850 M, [O2] = 0.560 M.

8. The following reaction has an equilibrium constant of 620 at a certain temperature. Calculate the equilibrium concentrations of all species if 4.5 mol of each component were added to a 3.0 L flask.

H2 (g) + F2 (g) « 2 HF (g)

8.  Ammonia undergoes hydrolysis according to the following reaction:

NH3 (aq) + H2O « NH4+ (aq) + OH- (aq) K = 1.8 x 10-5

Calculate [NH3], [NH4+] and [OH-] in a solution originally 0.200 M NH3.

9.  The equilibrium constant for the following reaction is 600°C is 4.0. Initially, two moles of CO and one mole of H2O were mixed in a 1.0 liter container. Determine the concentration of all species at equilibrium.

CO(g) + H2O(g) « CO2 (g) + H2 (g)

10. If 5.0 moles of O2 and 4.0 moles of NO were entered into an empty 1.0 liter flask, calculate the equilibrium constant if the amount of NO2 found at equilibrium was 1.5 moles.

11. If the equilibrium constant for the following reaction is 0.10, determine the final concentration of ICl, if 4.0 moles of I2 and Cl2 were entered initially into an empty 1.0 liter flask.

12. The reaction of carbon disulfide with chlorine is as follows:

CS2 (g) + 3 Cl2 (g) « CCl4 (g) + S2Cl2 (g) DH = -238 kJ

Predict the effect of the following changes to the system on the direction

of equilibrium.

a.  The pressure on the system is doubled by halving the volume.

b.  CCl4 is removed as it is generated.

c.  Heat is added to the system.

13. The reaction of nitrogen gas with hydloric acid is as follows:

N2 (g) + 6 HCl (g) « 2 NH3 (g) + 3 Cl2 (g) DH = 461 kJ

Predict the effect of the following changes to the system on the direction

of equilibrium

a.  Triple the volume of the system.

b.  The amount of nitrogen is doubled.

c.  Heat is added to the system.

Sometimes it’s our fault that things are out of balance.

Calculate the Equilibrium constant (Keq) of the following reactions:

14. Given the equilibrium system: PCl5(g)=> PCl3(g) + Cl2(g) The system is analyzed at a certain temperature and the equilibrium concentrations are as follows: [PCl5] = 0.32 M, [PCl3] = 0.40 M and the [Cl2] = 0.40 M. Calculate the Keq for this reaction at the temperature this was carried out

15. The equilibrium equation for the formation of ammonia is: N2(g) + 3H2(g) => 2NH3(g) In an equilibrium mixture at 200 °C, the concentrations were found to be as follows: [N2] = 2.12M, [H2] = 1.75M and [NH3] = 84.3M Notice the 3 sd’s in all your data. Calculate the value of the Equilibrium Constant for this reaction at 200°C.

16. At 200°C, the Keq for the reaction: N2(g) + 3H2(g)=> 2NH3(g) is 625 If the [N2] = 0.030 M, and the [NH3] = 0.12 M, at equilibrium, calculate the equilibrium [H2].