Question

The reaction favoured at low pressure is

• A. $H _{2}(g)+ I _{2}(g) \rightleftharpoons 2 HI (g)$
• B. $PCl _{5}(g) \rightleftharpoons PCl _{3}(g)+ Cl _{2}(g)$
• C. $N _{2}(g)+ O _{2}(g) \rightleftharpoons 2 NO (g)$
• D. $N _{2}(g)+3 H _{2}(g) \rightleftharpoons 2 NH _{3}(g)$

Answer 1

Answer: (B)

At equilibrium, low pressure favours those reactions which are accompained by increase in total number of moles and high pressure favours those reactions which take place with decrease in total number of moles. However, pressure has no effect on an eqilibrium reaction which proceeds with no change in total number of moles.
Hence, reaction
$PCl _{5}(g) \rightleftharpoons PCl _{3}(g)+ Cl _{2}(g)$
is favoured by low pressure.