Decomposition of limestone is industrially important in the manufacture of quicklime. In a lime kiln, calcium carbonate decomposes according to the balanced chemical equation
CaCO3(s) ⇌ CaO(s) + CO2(g).
At a fixed temperature, the system is allowed to reach equilibrium under a total pressure low enough that only the listed substances are present.
(a) Write the equilibrium‐constant expression Kp for the reaction.
(b) Give a particle‐level justification for omitting any species from your expression, explicitly referring to how their thermodynamic activities differ from those of gaseous species under the stated conditions.