The Haber’s process for the manufacture of ammonia is usually carried out at about 500°C. If a temperature of about 250°C was used instead of 500°C.

The rate of formation of ammonia would be too slow.

The correct answer is option 4. The rate of formation of ammonia would be too slow.

The Haber's process involves the synthesis of ammonia (\(NH_3\)) from nitrogen (\(N_2\)) and hydrogen (\(H_2\)) gases:

\(N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) \)

This reaction is exothermic, meaning it releases heat. According to Le Chatelier's principle, lowering the temperature favors the exothermic reaction direction.

Effects of Lower Temperature (250°C)

Equilibrium Position:  At 250°C, the equilibrium will shift to favor the formation of ammonia (\(NH_3\)) because the reaction is exothermic. This means the equilibrium constant (\(K\)) for the forward reaction will increase at lower temperatures.

Rate of Reaction: However, the rate at which ammonia forms at 250°C will be slower compared to 500°C. This is because lower temperatures reduce the kinetic energy of molecules, resulting in fewer effective collisions and slower reaction rates. The rate of formation of \(NH_3\) molecules from \(N_2\) and \(H_2\) molecules will be too slow to achieve a practical rate of production necessary for industrial processes.

(4) The rate of formation of ammonia would be too slow: The statement is correct.  At 250°C, while the equilibrium favors the formation of \(NH_3\), the rate at which \(NH_3\) forms would be significantly slower. This is due to the lower temperature reducing the kinetic energy of reactant molecules, resulting in fewer effective collisions and slower reaction rates.

Therefore, the correct answer is (4) The rate of formation of ammonia would be too slow. This correctly reflects the kinetic considerations of the Haber's process at a lower temperature, where although equilibrium conditions may favor \(NH_3\) formation, the actual rate of production would be impractically slow for industrial purposes.