Question

State Le-chatelier's principle and apply it to the following equilibrium.
$N_{2_{\left(g\right)}}+3H_{2_{\left(g\right)}}\rightleftharpoons 2N{H}_{3_{\left(g\right)}};△H=-92.0KJ$

Answer 1

Le Chatelier's principle:
If an external stress is applied to a reacting system at equilibrium, the system will adjust itself in such a way that the effect of the stress is reduced.
$N_{2_{\left(g\right)}}+3H_{2_{\left(g\right)}}\rightleftharpoons 2N{H}_{3_{\left(g\right)}};△H=-92.0KJ$
The forward reaction is endothermic ( as the enthalpy change is negative) and the reverse reaction is exothermic. If the temperature of system is increased, the equilibrium will shift from left to right. So more and more of N${}_2$ and H${}_2$ will be converted to NH${}_3$. The yield of NH${}_3$ will increase at high temperature. The decrease in temperature will favor the reverse reaction.
In the forward reaction, the number of moles decreases and in the reverse reaction, the number of moles increases. With increase in the pressure (by reducing the volume at constant temperature), the forward reaction is favored as the number of moles will decrease. This will increase the yield of NH${}_3$. When pressure is decreased, the reverse reaction is favored.