Chemistry Equilibrium ETEA 2019
PMDC Verified Question 81 of 102
Consider the reversible reaction. \( \text{N}_{2(g)} + 3\text{H}_{2(g)} \rightleftharpoons 2\text{NH}_{3(g)} + \text{Heat} \)

The yield of \( \text{NH}_3 \) will be maximum at:
A
High temperature and low pressure
B
High temperature and high pressure
C
Low temperature and low pressure
D
Low temperature and high pressure
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Low temperature and high pressure
Concept:

Le Chatelier's Principle dictates optimal conditions for the Haber process based on thermodynamics and stoichiometry.

Formula:

$$ \text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3 \quad \Delta H < 0, \Delta n = -2 $$

Solution:

  • The reaction produces heat (exothermic). Decreasing the temperature shifts the equilibrium forward to replace lost heat, yielding more \( \text{NH}_3 \).


  • The reaction goes from 4 moles of gas to 2 moles of gas. Increasing pressure favors the side with fewer moles of gas to reduce pressure. Thus, high pressure shifts it forward.


  • Therefore, maximum yield requires Low Temperature and High Pressure.


Why other options are incorrect:

High temperature would shift the reaction backwards. Low pressure would favor the side with more moles (reactants).

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