Question

For reaction, $N_2\left(g\right)+3H_2\left(g\right)\rightleftharpoons 2N{H}_3\left(g\right),$ following graph is obtained:

The change applied at $t=40sec$ is possibly :

• A. $H_2\left(g\right)$ is added at constant temperature and pressure
• B. Temperature is increased
• C. A suitable catalyst is added
• D. Pressure on the system is decreased suddenly at constant temperature

Answer 1

The correct option is D Pressure on the system is decreased suddenly at constant temperature

According to Le Chatelier's principle,
$N_2\left(g\right)+3H_2\left(g\right)\rightleftharpoons 2N{H}_3\left(g\right)$
(A) If $H_2\left(g\right)$ is added, reaction will shift in forward direction, hence amount of $H_2$ will decrease (not increase).
(B) Process is exothermic but still reaction is favorable at high temperature ($\approx 700K)$, so by increasing temperature, forward shift will be there.
(C) No effect of catalyst on the amount $H_2.$
(D) By decreasing pressure, the concentration of all the species decrease suddenly including $\left[H_2\right]$, then the reaction will shift in a direction where number of gaseous moles will increase (backward shift) . Hence, amount of $H_2$ increases again and reaches equilibrium.