A system is described as follows - HSC - SSCE Chemistry - Question 8 - 2022 - Paper 1

To derive the equilibrium expression, we start with the balanced equation:

$2NaHCO₃(s) ⇌ Na₂CO₃(s) + CO₂(g) + H₂O(g)$

In the equilibrium expression, we only consider the concentrations of gaseous and aqueous species, while excluding solids. Therefore, the equilibrium constant expression, $K_{eq}$, can be formulated as follows:

K_{eq} = rac{[CO₂][H₂O]}{[Na₂CO₃]}

This corresponds to Option B in the list of choices provided.