The equilibrium constant KcAQA A-Level Chemistry: Mind map

Exam questions on The equilibrium constant Kc

1. Nitrogen and hydrogen are sealed in a vessel at 500 K and form ammonia: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). When equilibrium is reached, the concentrations are [N₂] = 0.40 mol dm⁻³, [H₂] = 0.20 mol dm⁻³ and [NH₃] = 0.16 mol dm⁻³.
   Calculate the value of Kc for this reaction at 500 K, including its units.2 marks
2. Ethanoic acid and ethanol react in the presence of a small amount of sulfuric acid catalyst: CH₃COOH(l) + C₂H₅OH(l) ⇌ CH₃COOC₂H₅(l) + H₂O(l). At room temperature the equilibrium constant Kc for this reaction is 4.0.
   A mixture of 1.00 mol of ethanoic acid and 1.00 mol of ethanol is left to reach equilibrium at room temperature. Calculate the amount, in mol, of ethyl ethanoate present at equilibrium.2 marks
3. Dinitrogen tetraoxide, a colourless gas, is in equilibrium with nitrogen dioxide, a brown gas: N₂O₄(g) ⇌ 2NO₂(g), ΔH = +57 kJ mol⁻¹. A sealed 2.00 dm³ vessel initially contains 0.0600 mol of N₂O₄ only. It is held at a fixed temperature until equilibrium is reached, when 0.0800 mol of NO₂ is present.
   State and explain the effect of increasing the temperature on the value of Kc, and state the effect on Kc of increasing the pressure by compressing the vessel.3 marks