In the Haber process for ammonia synthesis, N2(g) + 3H2(g) ⇌ 2NH3(g), the reaction is exothermic. The process uses an iron catalyst and a temperature of about 450°C. Which of the following best explains why a temperature higher than the optimum for equilibrium is used?
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Correct answer
B. To increase the rate of reaction to a commercially acceptable level
Principle or equation
For an exothermic reaction, lower temperatures favor product formation according to Le Chatelier's principle, but lower temperatures also slow the reaction rate. A compromise temperature is used to achieve a reasonable rate while maintaining a moderate yield.
Why this answer is correct
The Haber process uses a temperature of about 450°C, which is higher than the temperature that would maximize equilibrium yield (lower temperature would give higher yield). The higher temperature increases the rate of reaction, making the process economically viable. The catalyst (iron) works effectively at this temperature. The yield is not maximized, but the rate is acceptable.
Example
At 450°C, the yield of ammonia is about 15-25% per pass, but the rate is fast enough for industrial production.
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