Final answer:
The reaction between nitrogen and hydrogen to form ammonia is exothermic, so increasing the temperature favors the reverse reaction, reducing the yield of ammonia despite accelerating the reaction rate.
Step-by-step explanation:
The reaction between nitrogen (N₂) and hydrogen (H₂) to form ammonia (NH₃) is known as the Haber-Bosch process. This is an exothermic reaction, as indicated by the negative change in enthalpy (ΔH = -92.2 kJ):
N₂(g) + 3H₂(g) → 2NH₃(g)
When the temperature is increased, the rate at which ammonia is formed does increase, but it also affects the equilibrium constant (Keq). High temperatures favor the reverse reaction due to the exothermic nature of ammonia synthesis, leading to lower yields of NH₃. This demonstrates the trade-off between reaction kinetics (rate of reaction) and thermodynamics (spontaneity and equilibrium position).
At temperatures above 463 K, the reactants are favored over the products. Therefore, although a higher temperature could speed up the reaction, it reduces the overall amount of ammonia produced. This is a classic challenge that chemical engineers must address, balancing the desire for a faster reaction with the thermodynamic limits imposed by high temperatures.