Le Chatelier application — ammonia synthesis N2 + 3 H2 ⇌ 2 NH3: How does fractional conversion change with increasing pressure at constant temperature?

Difficulty: Easy

Correct Answer: Increases

Explanation:


Introduction / Context:
Ammonia synthesis is a flagship example of equilibrium manipulation in heterogeneous catalysis. Pressure, temperature, and composition are tuned to favor ammonia formation while maintaining practical rates over iron based catalysts.


Given Data / Assumptions:

  • Balanced reaction: N2 + 3 H2 ⇌ 2 NH3.
  • Temperature is held constant.
  • Ideal gas behavior approximation for qualitative reasoning.


Concept / Approach:
Total gas moles decrease from 4 to 2 upon forming ammonia. By Le Chatelier principle, increasing pressure shifts equilibrium toward the side with fewer moles, hence promoting ammonia formation and increasing fractional conversion of reactants to NH3 at a given temperature.


Step-by-Step Solution:
Count moles: reactants 4, products 2.Apply pressure increase: system minimizes the pressure change by shifting to fewer moles.Therefore equilibrium conversion to NH3 increases.


Verification / Alternative check:
Equilibrium constant Kp is fixed at a given temperature. The relation between Kp and partial pressures shows that higher total pressure allows compositions with higher ammonia partial pressure while satisfying Kp at equilibrium.


Why Other Options Are Wrong:
Decrease or no change contradict the effect of pressure on a reaction with a negative change in moles of gas; unpredictability is not correct since stoichiometry is sufficient for the qualitative conclusion.


Common Pitfalls:
Ignoring the simultaneous effect of temperature on Kp; although high pressure favors NH3, too high a temperature reduces Kp even if it speeds kinetics.


Final Answer:
Increases

Discussion & Comments

No comments yet. Be the first to comment!
Join Discussion