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Using Le Chatelier’s principle, justify the choice of temperature and pressure conditions used to optimise the yield in the Haber process. - HSC - SSCE Chemistry - Question 23 - 2008 - Paper 1
Question 23
Using Le Chatelier’s principle, justify the choice of temperature and pressure conditions used to optimise the yield in the Haber process.
Worked Solution & Example Answer:Using Le Chatelier’s principle, justify the choice of temperature and pressure conditions used to optimise the yield in the Haber process. - HSC - SSCE Chemistry - Question 23 - 2008 - Paper 1
Step 1
Justify the choice of temperature conditions
Answer
In the Haber process, the reaction to produce ammonia is exothermic. According to Le Chatelier’s principle, increasing the temperature shifts the equilibrium position to the left, favoring the production of reactants (nitrogen and hydrogen). Therefore, lower temperatures are generally preferred to maximize the yield of ammonia. However, very low temperatures can slow down the reaction rate significantly, so a compromise temperature around 400-500°C is usually employed to ensure a reasonable rate while still promoting a good yield.
Step 2
Justify the choice of pressure conditions
Answer
The production of ammonia from nitrogen and hydrogen involves a decrease in the number of gas moles, as 1 mole of nitrogen and 3 moles of hydrogen produce 2 moles of ammonia. Applying Le Chatelier’s principle, increasing the pressure favors the direction of the reaction that produces fewer gas moles, which in this case is the formation of ammonia. As such, higher pressures (around 200 atmospheres) are used in the Haber process to optimize yield while maintaining manageable reaction conditions.