The model uses a few dozen molecules and real thermodynamics for N2 + 3H2 ⇌ 2NH3 (ΔH = −92 kJ/mol). The counts are a sample, so the percentages jump in steps; the trends (hotter gives less ammonia, higher pressure gives more) match the Haber process.
- What is Le Chatelier’s principle?
- Le Chatelier’s principle says that when a system at equilibrium is disturbed, it shifts in the direction that partly undoes the change. Raise the temperature of an exothermic reaction and it moves toward the reactants; add more pressure and it moves toward the side with fewer gas molecules; add a reactant and it moves toward the products.
- Why are the Haber process conditions 450 °C and 200 atm?
- Equilibrium favours ammonia at low temperature and high pressure, but low temperature makes the reaction too slow to be practical. About 450 °C gives a useful rate, 200 atm raises the yield, and an iron catalyst speeds the reaction up without changing the equilibrium position. The result is a compromise between yield and speed, not the best possible yield.
- Does a catalyst change the equilibrium position?
- No. An iron catalyst speeds up the forward and reverse reactions by the same factor, so the mixture reaches equilibrium sooner, but the final amounts (and K) are the same. A catalyst changes the time, not the position.
- What is the equilibrium constant Kc?
- For N2 + 3H2 ⇌ 2NH3, Kc = [NH3]² ÷ ([N2][H2]³), using concentrations at equilibrium. Kc depends only on temperature: it is larger when products are favoured. For this exothermic reaction Kc falls as the temperature rises.
- Why does high pressure increase the ammonia yield?
- Four gas molecules (1 N2 and 3 H2) become two molecules of NH3. Compressing the mixture raises the pressure, so the equilibrium shifts toward the side with fewer gas molecules, which is NH3.