10. Answer any two of the parts (a), (b) and (c) - Leaving Cert Chemistry - Question 10 - 2007

To find the equilibrium constant K_c, we first need the initial and equilibrium concentrations of the gases:

• Initial moles of N₂ = 3 mol, H₂ = 9 mol in a 1 L vessel:
  • Initial concentration of N₂: 3 mol/L
  • Initial concentration of H₂: 9 mol/L

At equilibrium, we have:

• Concentration of NH₃ = 2 mol/L

Using the stoichiometry, the change in concentration:

• N₂: 3 - x = 3 - 2/2 = 3 - 1 = 2 mol/L
• H₂: 9 - 3x = 9 - 3(2/2) = 9 - 3 = 6 mol/L

Substituting these values into the equilibrium expression:

$K_c = \frac{[2]^2}{[2][6]^3} \rightarrow \frac{4}{2\times216} = 0.009$

Thus, the value of K_c = 0.009.

An increase in pressure would lead to an increase in the yield of ammonia. According to Le Chatelier's principle, the system will shift in the direction that reduces the number of gas molecules to counteract the change in pressure.

In this case, the reaction:

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

has 4 moles of gas on the reactants side (1 N₂ + 3 H₂) and 2 moles of gas on the products side (2 NH₃). Therefore, increasing the pressure will shift the equilibrium to the right, favoring the production of ammonia and increasing its yield.