The following reaction occurs in the Blast furnance where iron ore is reduced to iron metal
Fe₂O₃₍ₛ₎+3CO_((g))⇌ Fe₍ₗ₎+3CO_(2(g))
Using the Le-chatelier's principle, predict which one of the following will not disturb the equilibrium.

Solution

Chemistry ma’am · 3 steps

Solids never appear in K, so adding more solid Fe₂O₃ cannot push the equilibrium anywhere.

1. Write K. Pure solids and liquids have a fixed concentration (activity 1), so they are left out of the equilibrium constant. Only the two gases appear.

   K_c = [CO₂]³/[CO]³

2. Changing the gases. Adding or removing CO or CO₂ changes a term in this ratio. The reaction quotient Q no longer equals K, so the system shifts to restore it.

   Change	Appears in K?	Effect
   Add CO₂	Yes	Q > K, shifts backward
   Remove CO	Yes	Q > K, shifts backward
   Add Fe₂O₃ (solid)	No	Q stays equal to K, no shift
   Remove CO₂	Yes	Q < K, shifts forward

3. So. Extra solid Fe₂O₃ does not change any term in K, so the equilibrium is not disturbed. The answer is (c).

The idea to keep. In heterogeneous equilibria, only gases and dissolved species count. Adding or removing a pure solid or liquid (as long as some is present) never shifts the equilibrium.

Answer from the NTA final answer key. Solution by PrepWiser.