Which of the following equilibria is unaffected by a pressure change?
- 2NaCI(s) ↔ 2Na (I) + CI2(g)
-
H 2(g) + I2(g) ↔ 2HI(g)
- 2O3(g) ↔ 3O2(g)
- 2NO2(g) ↔ N2O4(g)
The correct answer is: B
Explanation
The equilibrium concentrations of the products and reactants do not directly depend on the total pressure of the system. The only thing we consider are the gaseous substances. This means we consider the total number of gaseous substances on the reactant side and the total number of gaseous substances on the product side. The side with the lesser number of moles will be favoured by an increase in pressure because the equilibrium position will shift to that side and vice versa. However, if the number of moles of gaseous reactants is equal to the number of moles of gaseous products, pressure has no effect on equilibrium, as seen in option B only where the total number of moles gaseous reactant is 2 just as it is also for the gaseous products.