Kp and calculating equilibrium constantsEdexcel A-Level Chemistry: Subtopic test

1. 1
   Dinitrogen tetroxide dissociates reversibly: N₂O₄(g) ⇌ 2NO₂(g). In an experiment at 350 K the equilibrium mixture contained 0.40 mol of N₂O₄ and 0.20 mol of NO₂, and the total pressure was 3.0 atm.

   (a)

   What is the partial pressure of NO₂ in the equilibrium mixture?

   [1 mark]

   • A0.33 atm
   • B2.0 atm
   • C0.20 atm
   • D1.0 atm

   (b)

   Which is the correct expression for Kp for this equilibrium?

   [1 mark]

   • A$K_p = \frac{p_{\mathrm{N_2O_4}}}{p_{\mathrm{NO_2}}^2}$
   • B$K_p = \frac{p_{\mathrm{NO_2}}}{p_{\mathrm{N_2O_4}}}$
   • C$K_p = \frac{p_{\mathrm{NO_2}}^2}{p_{\mathrm{N_2O_4}}}$
   • D$K_p = \frac{[\mathrm{NO_2}]^2}{[\mathrm{N_2O_4}]}$

   (c)

   Calculate the partial pressure of N₂O₄ and the value of Kp for this equilibrium, including its units.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a sealed 2.00 dm³ vessel at 700 K, 1.00 mol of hydrogen and 1.00 mol of iodine were mixed and allowed to reach equilibrium: H₂(g) + I₂(g) ⇌ 2HI(g). At equilibrium the vessel contained 0.220 mol of hydrogen.

   (a)

   What amount of iodine is present at equilibrium?

   [1 mark]

   • A0.780 mol
   • B0.220 mol
   • C1.56 mol
   • D0.110 mol

   (b)

   What are the units of Kc for this equilibrium?

   [1 mark]

   • AIt has no units
   • Bmol dm⁻³
   • Cmol⁻¹ dm³
   • Dmol² dm⁻⁶

   (c)

   Calculate the equilibrium concentration of hydrogen iodide.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A mixture of 0.800 mol of sulfur dioxide and 0.600 mol of oxygen was sealed in a 2.00 dm³ vessel at 1000 K and allowed to reach equilibrium: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g). At equilibrium the vessel contained 0.600 mol of sulfur trioxide.

   (a)

   Calculate the amounts of SO₂ and O₂ at equilibrium and the equilibrium concentration of each of the three gases.

   [3 marks]

   (b)

   Calculate the value of Kc for this equilibrium at 1000 K, including its units.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Two equilibria are studied. System 1 is the heterogeneous equilibrium C(s) + CO₂(g) ⇌ 2CO(g) at 1100 K. At equilibrium the total pressure is 2.00 atm and 70.0% of the gas, by amount, is carbon monoxide. System 2 is PCl₅(g) ⇌ PCl₃(g) + Cl₂(g). 1.00 mol of PCl₅ is heated in a vessel and, at equilibrium, 0.400 mol of PCl₅ remains and the total pressure is 3.00 atm.

   (a)

   For System 1, deduce the expression for Kp and calculate its value, including units.

   [6 marks]

   (b)

   For System 2, calculate the value of Kp, including its units.

   [6 marks]

   Total for question 4: 12 marks

End of questions