The reaction between nitrogen and hydrogen is exothermic. If nitrogen and hydrogen were reacted at 150 atm pressure and 300 °C, without a catalyst, some ammonia would be formed. In the Haber process a pressure of 150 atm and a temperature of 450 °C are used, in the presence of an iron catalyst. Explain why the conditions used in the Haber process are better than the first set of conditions for the manufacture of ammonia – 9026

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1. When the temperature increases, the particles move faster because they have more energy. This makes collisions between particles happen more often, and also the collisions have enough energy to overcome the activation energy. So the reaction reaches equilibrium faster.

   However, in a reversible reaction like the Haber process, a higher temperature can cause the equilibrium to shift. Since the forward reaction is exothermic, a rise in temperature favors the reverse (endothermic) reaction, so the equilibrium shifts to the left. This means the yield of ammonia decreases, because more of it breaks down into nitrogen and hydrogen.

   Using a catalyst helps the reaction reach equilibrium faster, because it lowers the activation energy. It increases the rate of both the forward and backward reactions, but it does not affect the position of equilibrium, so the yield stays the same.

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