Question

Which of the following reactions will be favored in the forward direction when the pressure in a system is increased?
$I.CaC{O}_3\left(s\right)\rightleftharpoons CaO\left(s\right)+CO\left(g\right)$
$II.Mg\left(s\right)+2H_{2}O\left(g\right)\rightleftharpoons Mg\left(OH{)}_2\right(aq)+H_2(g)$
$III.2N_2{O}_5\left(g\right)\rightleftharpoons O_2\left(g\right)+4N{O}_2\left(g\right)$

• A. II only
• B. I only
• C. I and II only
• D. I, II, and III

Answer 1

The correct option is A II only

Finding $\Delta n_g$ in I, II, and III
In I : $\Delta n_g=1$
In II : $\Delta n_g=1-2=-1$
In III: $\Delta n_g=5-2=3$

In II: As the pressure is increased, $\frac{n_g}{V}\uparrow$, the reaction goes where $n_g$ decreases. For $\Delta n_g<0$, it decreases in the forward direction.
So when $\Delta n_g<0$, and $P\uparrow$, the reaction goes in forward direction.