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.

(i) COCl₂ (g) ⇌CO (g) + Cl₂ (g)

(ii) CH₄ (g) + 2S₂ (g) ⇌CS₂ (g) + 2H₂S (g)

(iii) CO₂ (g) + C (s) ⇌ 2CO (g)

(iv) 2H₂ (g) + CO (g) ⇌ CH₃OH (g)

(v) CaCO₃ (s) ⇌CaO (s) + CO₂ (g)

(vi) 4 NH₃ (g) + 5O₂ (g) ⇌ 4NO (g) + 6H₂O(g)

According to Le Chatelier’s principle, an increase in pressure applied to the system at equilibrium favours the reaction in the direction which takes place with a decrease in a total number of moles. If there is no change in the number of moles of gases in a reaction, a pressure change does not affect the equilibrium.

Hence, reactions affected will be those in which number of moles of products (n_p) is not equal to number of moles of reactants (n_p )

∴ n_p ≠ n_r. Hence, the reactions (i), (iii), (iv), (v) and (vi) will be affected. By applying Le Chatelier’s principle, we can predict the direction. In general,

⇒The reaction will go to the left if n_p > n_r

⇒The reaction will go tp the right if n_p < n_r

(i)COCl₂ (g) ⇌CO (g) + Cl₂ (g)

Number of moles of products (n_p)= 2

Number of moles of reactants (n_r) = 1

∴ n_p > n_r

According to Le Chatelier’s principle, the reaction will proceed in the backward reaction.

(ii) CH₄ (g) + 2S₂ (g) ⇌CS₂ (g) + 2H₂S (g)

Number of moles of products (n_p)= 3

Number of moles of reactants (n_r) = 3

∴ n_p = n_r

According to Le Chatelier’s principle, the reaction will not be affected by the pressure.

(iii) CO₂ (g) + C (s) ⇌ 2CO (g)

Number of moles of products (n_p)= 2

Number of moles of reactants (n_r) = 1

∴ n_p > n_r

According to Le Chatelier’s principle, the reaction will proceed in the backward direction.

(iv) 2H₂ (g) + CO (g) ⇌ CH₃OH (g)

Number of moles of products (n_p)= 1

Number of moles of reactants (n_r) = 3

∴ n_p < n_r

According to Le Chatelier’s principle, the reaction will proceed in the forward direction.

(v) CaCO₃ (s) ⇌CaO (s) + CO₂ (g)

Number of moles of products (n_p)= 2

Number of moles of reactants (n_r) = 1

∴ n_p > n_r

According to Le Chatelier’s principle, the reaction will proceed in the backward direction.

(vi) 4 NH₃ (g) + 5O₂ (g) ⇌ 4NO (g) + 6H₂O(g)

Number of moles of products (n_p)= 10

Number of moles of reactants (n_r) = 9

∴ n_p > n_r

According to Le Chatelier’s principle, the reaction will proceed in the backward direction.