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In the Haber process, the synthesis of ammonia from nitrogen and hydrogen is an equilibrium reaction represented by the equation:
[ N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) ]
According to Le Chatelier's principle, when a system at equilibrium is subjected to a change in conditions (such as pressure), the equilibrium will shift in a direction that counteracts that change. In this reaction, there are two moles of gas on the reactant side (one mole of nitrogen and three moles of hydrogen) and only two moles of gas on the product side (two moles of ammonia).
When high pressure is applied, the system will respond by shifting the equilibrium towards the side with fewer gas moles, which in this case is the production of ammonia. Therefore, increasing the pressure favors the formation of ammonia, leading to a higher yield. This is why high-pressure conditions are selected for the Haber process, as it effectively increases the production of ammonia by shifting the equilibrium position towards the products.