Final answer:
In summary, in the given scenarios, entropy increases when a solid becomes a gas, whereas it decreases when gases combine to form a solid or fewer gas molecules. The change is determined by the state of matter and the number of molecules involved in the reaction.
Step-by-step explanation:
The processes described relate to chemical reactions and phase changes and their effect on the entropy of the system. Entropy is a measure of the disorder or randomness in a system, and chemical processes can either increase or decrease the entropy depending on the nature of the changes.
(a) CO₂ (s) → CO₂ (g): The entropy increases because the carbon dioxide is changing from a solid to a gas, and gases have higher entropy than solids.
(b) CaO (s) + CO₂ (g) → CaCO₃ (s): The entropy decreases as gas is converted to solid in the reaction, implying less disorder.
(c) HCl (g) + NH₃ (g) → NH₄Cl (s): This process decreases entropy because it involves the formation of a solid from gases.
(d) 2 SO₂ (g) + O₂ (g) → 2 SO₃ (g): The entropy likely decreases since three moles of reactant gases form two moles of product gas, even though all substances are in the gaseous state.
In general, entropy tends to increase when solids or liquids are converted to gases, when the number of product molecules is greater than the number of reactant molecules (exceptions exist), at higher temperatures, and when solutions form from solids.