The production of ammonia gas from nitrogen gas and hydrogen gas is spontaneous

Question

The production of ammonia gas from nitrogen gas and hydrogen gas is spontaneous under standard conditions as seen from the G° of -26.50 kJ/mol for the reaction. It is an exothermic process as seen from the H° of -46.19 kJ/mol for the reaction. Which of the following best describes why the commercial process for the production of ammonia is carried out at 400-500°C and around 200 atm in the presence of a catalyst?

a. The high pressure is needed to increase the rate of the reaction, the catalyst lowers the energy needed to break the nitrogen-nitrogen triple bond, and the high temperature increases the amount of ammonia made because it shifts the equilibrium towards the products. b. The high temperature and pressure increase the amount of ammonia made because they shift the equilibrium towards the products. The catalyst lowers the energy needed to break the strong hydrogen bond in the hyrdogen molecule. c. The high temperature is needed to increase the rate of the reaction, the catalyst lowers the energy needed to break the strong hydrogen bond in the hyrdogen molecule, and the high pressure increases the amount of ammonia made because it shifts the equilibrium towards the products. d. The high temperature and pressure increase the amount of ammonia made because they shift the equilibrium towards the products. The catalyst lowers the energy needed to break the nitrogen-nitrogen triple bond. e. The high temperature is needed to increase the rate of the reaction, the catalyst lowers the energy needed to break the nitrogen-nitrogen triple bond, and the high pressure increases the amount of ammonia made because it shifts the equilibrium towards the products.

Explanation / Answer

answer :

e. The high temperature is needed to increase the rate of the reaction, the catalyst lowers the energy needed to break the nitrogen-nitrogen triple bond, and the high pressure increases the amount of ammonia made because it shifts the equilibrium towards the products.

haber process:

N2 (g) + 3 H2 (g) <-------------------> 2NH3 (g) , H° = -46.19 kJ/mol

for getting good yield of NH3 we have to use following conditions according to Lechatliers- principle

(1) reactant moles = 1+3 = 4

      product moles = 2

pressure increases the equilibrium always shifts to the direction where volume or number of moles decreses.

so in this reaction reaction moles 4-----------> 2 . to get better product high pressure is needed

    (2) forward reaction is exothermic reaction . so low temperatures are favoured. but at this temperature the rate of the reaction very slow. so optimum temperature is needed to increases the rate.

(3) even by providing high pressure and optimum temperature the rate is still low . so catalyst is needed to decrease the activation energy of the reacting molecules

note : pressure not affcted the rate . so a & d are excluded

        there is no hydrogens bonds in H2 or N2 so b&c are excluded

so only 'e' option correct

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