Ammonia is produced in the Haber process - AQA - GCSE Chemistry - Question 7 - 2022 - Paper 2

The equation shows that for every mole of nitrogen and three moles of hydrogen, two moles of ammonia are produced. Since all the reactants are converted into the desired product (NH₃), the atom economy is calculated as:

$\text{Atom Economy} = \frac{\text{Molar mass of desired product}}{\text{Total molar mass of reactants}} \times 100\%$

Substituting the molar masses:

• Molar mass of NH₃ = 17 g/mol
• Total molar mass of reactants = 28 g/mol (N₂) + 6 g/mol (from 3H₂) = 34 g/mol.

Thus,
$\text{Atom Economy} = \frac{17}{34} \times 100\% = 50\%$
However, considering the formation involves complete conversion into reactants without wastage, it is implied that the atom economy can be viewed as 100% for practical purposes in the context of synthesis.

In the Haber process, once ammonia (NH₃) is synthesized, the reaction mixture is cooled. The ammonia, being a gas at reaction temperature, will liquefy upon cooling, allowing it to condense. This cooling process permits the separation of ammonia from unreacted nitrogen and hydrogen, which remain in gaseous form, thus enabling the recovery of ammonia while continuously recycling the leftover gases back into the reactor.

To determine the percentage yield of ammonia at 450 °C and 500 atmospheres, we can extrapolate from Table 6.
Given that the yields are listed for certain pressures, we can make a linear estimate that the yield would increase as the pressure rises, resulting in a yield close to:

• For 420 atmospheres, the yield is 43%.
  Assuming a slight increase in yield, we estimate that at 500 atmospheres, the percentage yield of ammonia might be approximately 45%.
  Using the graph plotted in Figure 5 would also assist in verifying this extrapolation.

The conditions for the Haber process are selected based on several factors to ensure economical production:

Rate of Reaction

• A temperature of 450 °C speeds up the reaction rate by increasing the frequency of effective collisions among reactants.
• High pressure (200 atmospheres) also promotes a higher rate of reaction by forcing gaseous reactants into closer proximity, leading to more effective collisions.
• The iron catalyst lowers the activation energy required, allowing the reaction to proceed at a faster rate without the need for excessively high temperatures.

Position of Equilibrium

• The exothermic nature of the forward reaction implies it favors lower temperatures, but higher temperatures enhance reaction speed.
• A pressure of 200 atmospheres favors forward reaction completion as it shifts the equilibrium to the right, producing more ammonia while maintaining efficient reaction rates.
• Ultimately, the chosen conditions represent a compromise between maximizing yield and maintaining a feasible rate of production, thus optimizing the overall economic viability of the Haber process.