Though kinetics of ammonia synthesis dictates the use of low temperature for high equilibrium conversion, yet it is kept moderately high (550°C), because at low temperature

ANS:A - rate of reaction is very low.

Keeping the temperature moderately high (around 550°C) in the Haber-Bosch process for ammonia synthesis, despite the kinetic preference for lower temperatures, is primarily due to the following reasons:

1. Rate of Reaction: At lower temperatures, the rate of the ammonia synthesis reaction decreases significantly. While lower temperatures favor higher equilibrium conversions according to Le Chatelier's principle, the slow reaction kinetics at these temperatures make the process economically unfeasible. Operating at moderately high temperatures allows for a reasonable rate of reaction while still achieving acceptable equilibrium conversions.
2. Pressure Requirement: Extremely low temperatures would require very high pressures to achieve reasonable conversion rates. This would necessitate the use of costly pressure vessels and safety measures to handle the high pressures involved. By operating at moderately high temperatures, the pressure requirement is reduced, making the process more economical.
3. Space Velocity: Lower temperatures result in lower space velocities (the rate at which reactants flow through the reactor), which can lead to decreased conversion efficiency. Operating at moderately high temperatures allows for a balance between reaction kinetics and space velocity, optimizing conversion efficiency while maintaining a practical reactor size.

In summary, while lower temperatures theoretically favor higher equilibrium conversions in the ammonia synthesis reaction, practical considerations such as reaction kinetics, pressure requirements, and space velocity dictate the use of moderately high temperatures (around 550°C) in industrial-scale ammonia production processes like the Haber-Bosch process.