Drill setup

For the equilibrium N2(g)+3H2(g)⇌2NH3(g), Kc = 0.060 at 500 K. Explain how Kc changes if pressure increases at constant temperature, and calculate Qc direction if [N2]=[H2]=[NH3]=0.10 mol dm−3.

7 marks · est. accuracy 72%

1. +1 mark

   State Kc expression: [NH3]² / ([N2][H2]³)

2. +2 marks

   Note Kc depends on T only — pressure does not change Kc

3. +2 marks

   Compute Qc = (0.10)² / ((0.10)(0.10)³) = 1000

4. +2 marks

   Compare Qc ≫ Kc → net reverse reaction

• · Common error: Saying Kc rises with pressure
• · Common error: Forgetting powers in Kc
• · Common error: Mixing Kp/Kc