Question

Question: In order to get the highest yield of NH3(g) in Haber process, should you use high or low temperature?

The answer in the textbook says lower temperature produces more yield of NH3(g) in Haber process since it is exothermic. Doesn't lower the temperature also lower the reaction rate which results lower yield? My teacher says higher temperature produces more NH3(g) even though the the reaction shifts to the reactant side.

Answer 1

Lower temperatures increase the yield of ammonia in the Haber process due to its exothermic nature. A catalyst is used to speed up reactions at moderate temperatures, balancing yield and reaction rate. The process also uses high pressure and removal of NH3 to favor product formation.

Step-by-step explanation:

In the Haber process for the production of ammonia (NH3), lower temperatures favor the formation of more ammonia due to the reaction being exothermic. However, even though lower temperatures increase the yield of ammonia by shifting the equilibrium to the product side, they also decrease the rate of reaction, resulting in a slower process. To address this, a catalyst is used to increase the rate of reaction at moderate temperatures. Additionally, applying a higher pressure and removing ammonia from the system as it forms also shifts the equilibrium towards more ammonia production.

Contrarily, higher temperatures increase the reaction rate but decrease the yield of ammonia because the reaction is exothermic and an increase in temperature favors the endothermic direction, which is the decomposition of ammonia back into nitrogen and hydrogen. Therefore, the Haber process typically operates at a compromise temperature that ensures both a reasonable reaction rate and a good yield of ammonia, which is within the range of 400-500 °C.