Question

Which of the following reactions will get affected by increasing the pressure? Also, mention whether change will cause the reaction to go into forward or backward direction.

1. \[\ce{COCl2 (g) ⇌ CO (g) + Cl2 (g)}\]
2. \[\ce{CH4 (g) + 2S2 (g) ⇌ CS2 (g) + 2H2S (g)}\]
3. \[\ce{CO2 (g) + C (s) ⇌ 2CO (g)}\]
4. \[\ce{2H2 (g) + CO (g) ⇌ CH3OH (g)}\]
5. \[\ce{CaCO3 (s) ⇌ CaO (s) + CO2 (g)}\]
6. \[\ce{4 NH3 (g) + 5O2 (g) ⇌ 4NO (g) + 6H2O(g)}\]

Answer 1

The reactions given in (i), (iii), (iv), (v), and (vi) will get affected by increasing the pressure.

The reaction given in (iv) will proceed in the forward direction because the number of moles of gaseous reactants is more than that of gaseous products.

The reactions given in (i), (iii), (v), and (vi) will shift in the backward direction because the number of moles of gaseous reactants is less than that of gaseous products.

Answer 2

Only those reactions will be affected by increasing the pressure in which the number of moles of the gaseous reactants and products is different (n_p ≠ n_r) (gaseous). With the exception of reaction (1); all the remaining five reactions will get affected by increasing the pressure. In general

• The reaction will go to the left if n_p> n_r.
• The reaction will go to the right if n_r > n_p .
  Keeping this in mind,

1. Increase in pressure will not affect equilibrium because n_p = n_r = 3.
2. Increase in pressure will favour backward reaction because n_p (2) > n_r (1)
3. Increase in pressure will favour backward reaction because n_p (10) > n_r (9)
4. Increase in pressure will favour forward reaction because n_p (1) < n_r (2)
5. Increase in pressure will favour backward reaction because n_p (2) > n_r(1)
6. Increase in pressure will favour backward reaction because n_p (1) > n_r (0).