On the basis of the $Le \ Chatelier$ principle,explain how temperature and pressure can be adjusted to increase the yield of ammonia in the following reaction: $N_{2(g)} + 3H_{2(g)} \rightleftharpoons 2NH_{3(g)}$; $\Delta H = -92.38 \ kJ \ mol^{-1}$. What will be the effect of the addition of argon to the above reaction mixture at constant volume?

(N/A) $1$. Effect of temperature: Since the reaction is exothermic $(\Delta H < 0)$,according to the $Le \ Chatelier$ principle,a low temperature favors the forward reaction to increase the yield of $NH_3$. However,very low temperatures make the reaction rate too slow. Thus,an optimum temperature of approximately $700 \ K$ is maintained.
$2$. Effect of pressure: The forward reaction involves a decrease in the number of moles ($4 \ mol$ of reactants to $2 \ mol$ of products). According to the $Le \ Chatelier$ principle,high pressure favors the forward reaction. Therefore,a high pressure of about $200 \ atm$ is used to increase the yield.
$3$. Effect of addition of argon: At constant volume,the addition of an inert gas like argon does not change the partial pressures or concentrations of the reacting species. Consequently,the equilibrium remains unaffected.