11This is because every exothermic rxn shifts its eqb in the backward direction when temp is increased..reason is simple..take two temperatures T1 N T2..T2>T1...put them in the Vant Hoff's Eqn..ul c why it backward rxn takes place.
Variation in Keq for the Equilibrium
N2 (g) + 3H2 (g) ↔ 2NH3 (g)
as a Function of Temperature
Temperature (°C) Keq
300 4.34 x 10–3
400 1.64 x 10–4
450 4.51 x 10–5
500 1.45 x 10–5
550 5.38 x 10–6
600 2.25 x 10–6
As the temperature increases, the equilibrium is shifted and hence, the amount of product drops dramatically according to the Van't Hoff equation. Thus one might suppose that a low temperature is to be used and some other means to increase rate. However, the catalyst itself requires a temperature of at least 400 °C to be efficient.
