Consider the reactions so2(g) → o2(g) + s(s) kc = 2.5 × 10−53 so3(g) → 1 2 o2(g) + so2(g) kc = 4.0 × 10−13 calculate kc for the reaction 2 s(s) + 3 o2(g) → 2 so3(g)

Answer is: Kc for the reaction is 1·10¹³⁰.
Chemical reaction 1: SO₂(g) → O₂(g) + S(s); Kc₁ = 2,5 × 10⁻⁵³.
Chemical reaction 2: SO₃(g) → 1/2 O₂(g) + SO₂(g); Kc₂ = 4,0 ×10⁻¹³.
Chemical reaction 3:  2S(s) + 3O₂(g) → 2SO₃(g); Kc₃ = ?.
We can get reaction 3 by summing reverse reaction  multiply with and reverse reactio 2 multiply with two.
Kc₃ = (1/Kc₁²) · (1/Kc₂²) = 1/(2,5 × 10⁻⁵³)² · 1/(4,0 ×10⁻¹³)².
Kc₃ = 1,6·10¹⁰⁵ · 6,25·10²⁴ = 1·10¹³⁰.