Question

Which of the following reactions will be favoured at low pressure?

• A. $N_2\left(g\right)+3H_2\left(g\right)\rightleftharpoons 2N{H}_3\left(g\right)$
• B. $H_2\left(g\right)+I_2\left(g\right)\rightleftharpoons 2HI\left(g\right)$
• C. $PC{l}_5\left(g\right)\rightleftharpoons PC{l}_3\left(g\right)+C{l}_2\left(g\right)$
• D. $N_2\left(g\right)+O_2\left(g\right)\rightleftharpoons 2NO\left(g\right)$

Answer 1

The correct option is C $PC{l}_5\left(g\right)\rightleftharpoons PC{l}_3\left(g\right)+C{l}_2\left(g\right)$

When the pressure is decreased, according to Le - chatelier principle, the equilibrium will shift in direction having more no. of gaseous moles, so that with the increase in number of moles, the total pressure increases to nullify the effect of reduced pressure.
So, the reaction to proceed in forward direction it should have more number of gaseous moles in the product side.
This is the favourable condition for the reaction, $PC{l}_5\left(g\right)\rightleftharpoons PC{l}_3\left(g\right)+C{l}_2\left(g\right)$
Hence, (c) is correct choice.