Question

Which of the following reactions proceed at low pressure?

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

Answer 1

The correct option is C $PC{l}_5\rightleftharpoons PC{l}_3+C{l}_2$

Pressure is one of the factors which affects the chemical equilibrium of the reversible system. If the pressure of the reacting species is increased then as per Le Chatelier's principle equilibrium shifts to reduce the pressure. The side of the reaction with a fewer number of gas molecules will be favored.

In the following given reaction,
$PC{l}_5\rightleftharpoons PC{l}_3+C{l}_2$
L.H.S has 1 mole and R.H.S has 2 moles
Thus, decrease in the pressure helps the reaction move in forward direction.