A student investigates the thermal decomposition of calcium carbonate in an open crucible at 298 K.
CaCO₃(s) → CaO(s) + CO₂(g)
Selected standard molar entropies at 298 K are listed below.
Species S° (J·mol⁻¹·K⁻¹)
CaCO₃(s) 92.9
CaO(s) 39.8
CO₂(g) 213.7
Assume all gases behave ideally and that solid phases are perfectly crystalline.
(1) Without performing any numerical calculation, state whether the standard entropy change ΔS° for the reaction is expected to be positive, negative, or approximately zero. Provide two distinct pieces of reasoning based on the balanced equation and the physical states of the species.
(2) Use the data in the table to calculate the numerical value of ΔS° at 298 K, including the correct sign and units.
(3) Explain whether the numerical result obtained in part (b) is consistent with the qualitative prediction given in part (a) and discuss the physical significance of the magnitude of the entropy change.