Final answer:
The sign of the entropy change depends on the changes in the number of particles and phase transitions in the reaction. In (a) and (b), the entropy change is negative as solid is formed, while in (c), the entropy change is positive due to the formation of more gaseous species.
Step-by-step explanation:
The sign of the entropy change can be predicted based on the changes in the number of particles and the phase transition that occur in the reaction.
(a) Na+(aq) + Cl-(aq) ⟶ NaCl(s): The entropy change is negative because the reaction involves the formation of a solid from aqueous ions, resulting in decreased dispersal of matter.
(b) 2Fe(s) + 3O₂(g) ⟶ Fe₂O₃(s): The entropy change is negative because the reaction involves the formation of a solid from elemental substances and gases, resulting in decreased dispersal of matter.
(c) 2C₆H₁₄(l) + 19O₂(g) ⟶ 14H₂O(g) + 12CO₂(g): The entropy change is positive because the reaction involves the formation of more gaseous species from a liquid and gas, resulting in increased dispersal of matter.