Question

In the manufacture of ammonia by Haber process high pressure is maintained because:

• A. all reactants and product are gases
• B. reaction is exothermic
• C. the moles of the product are less than the moles of reactants
• D. reaction is reversible reaction

Answer 1

Answer: (C)

the moles of the product are less than the moles of reactants

In the manufacture of ammonia by the Haber process, high pressure is maintained because the moles of the product is less than the moles of reactants.

$N_2\left(g\right)+3H_2\left(g\right)\rightleftharpoons 2{NH}_3\left(g\right)$

$\Delta n_g=2-(1+3)=-2$

$\Delta n_g<0$

When pressure is increased, the equilibrium will shift to the product side (which contains less number of moles of gaseous species). This nullifies the effect of the increase in pressure. Hence, more and more ammonia will be formed.

According to Le Chatelier's principle, when a system at equilibrium is disturbed, the position of the equilibrium shifts in a direction so that the effect of the change is nullified.