12. Chemical Equilibrium problems

1. Write the K expression for each of the following chemical equilibria.

1. 3/2 O₂(g) ⇄ O₃(g)
2. NH₃(g) + 5/4 O₂(g) ⇄ NO(g) + 3/2 H₂O(g)
3. CH₄(g) + 2 O₂(g) ⇄ CO₂(g) + 2 H₂O(g)
4. CO(g) + 1/2 O₂(g) ⇄ CO₂(g)
5. 1/2 N₂(g) + 1/2 O₂(g) ⇄ NO(g)
6. CH₄(g) + 4 Cl₄(g) ⇄ CCl₄(l) + 4 HCl(g)
7. 2 NaHCO₃(s) ⇄ Na₂CO₃(s) + CO₂(g) + H₂O(g)
8. 2 H₂S(g) + SO₂(g) ⇄ 3 S(s) + 2 H₂O(l)

2. For the production of methanol by the reaction CO(g) + 2H₂(g) ⇄ CH₃OH(g), the enthalpy change of the reaction is ΔH° = -25 kJ/mol.  which of the following conditions favours the production of methanol?

1. high pressure and high temperature
2. high pressure and low temperature
3. low pressure and high temperature
4. low pressure and low temperature.

3. Calculate the relative activity of each of the following at a temperature of 25℃.

1. Pure solid Carbon (graphite) at a pressure of 100. kPa.
2. Oxygen gas O₂ at a partial pressure of 23.0 kPa.
3. Methane gas CH₄ at a partial pressure of 221. kPa
4. Pure liquid water H₂O at a pressure of 100. kPa.

[1.00, 0.230, 2.21, 1.00]

4. Calculate the relative activity of each of the following at a temperature of 50.0℃

1. Pure solid zinc metal at a pressure of 100. kPa.
2. Nitrogen gas as a partial pressure of 7.54 kPa.
3. Sulfur trioxide gas, SO₃, at a partial pressure of 72.3 kPa.
4. Pure liquid lead benzene C₆H₆ at a pressure of 100. kPa.

[1.00 0.0754, 0.723, 1.00]

5. Calculate the relative activity of each of the following at a temperature of  300. ℃

1. Pure solid iron metal as a pressure of 100. kPa.
2. Water vapour H₂O at a partial pressure of 310. kPa.
3. Sulfur dioxide gas SO₂ at a partial pressure of 101.3 kPa.
4. Pure liquid lead metal Pb at a pressure of 100. kPa.

[1.00, 3.10, 1.013, 1.00]

6. In an equilibrium mixture of SO₂, SO₃, and O₂ at a particular temperature, The partial pressure of SO₂ is half the partial pressure of SO₃ and the partial pressure of oxygen is 15.5 kPa.   What is the equilibrium constant?
SO₂(g) + 1/2 O₂(g) ⇄ SO₃(g)

[5.08]

7. A bulb contains an equilibrium mixture of SO₂, SO₃, and O₂ at a fixed temperature, enough argon is pumped into the bulb to double the total pressure in the bulb. What effect will this have on the pressure of SO₃?

8. The equilibrium constant for the reaction N₂(g) + 3 H₂(g) ⇄ 2 NH₃(g) is 6.9×10^-4 at 500℃.  If the volume of a vessel containing some of the equilibrium mixture is halved at constant temperature, what is the new value for the equilibrium constant?

[NC]

9. The following table summarizes some experimental measurements of the equilibrium
2 SO₂(g) + O₂(g) ⇄ 2 SO₃(g)
at a temperature of 1000.K in a series of experiments, starting with different initial amounts of the three substances involved.  The partial pressures of the gases are expressed in atmospheres. (1 atm = 101.325 kPa)

1. for each experiment, calculate K_p using atmospheres pressure units and then calculate the average value of K_p for the whole set.
2. From the average value of K_p, calculate the value of K, the thermodynamic equilibrium constant.

[3.40 atm^-1, 3.36]

10. Nitric acid NO can be formed from atmospheric oxygen and nitrogen in the following reaction, for which   K = 7×10^-16 at 25℃.    1/2 N₂(g) + 1/2 O₂(g) ⇄ NO(g).

1. Estimate the partial pressure of NO in the atmosphere, given the partial pressures of p(O₂) = 20. kPa and p(N₂) = 80 kPa.
2. The heat of formation of NO is Δ_fH° = +90.25 kJ/mol.  Would you expect the partial pressure of NO in the air passing through a flame to be larger, the same, or smaller than in air at room temperature.

[3×10^-11]