Final answer:
The sign of entropy change (ΔS) for a chemical reaction indicates the change in disorder. It can be positive, negative, or zero, depending on whether the disorder increases, decreases, or remains the same, and it is calculated based on the states of reactants and products.
Step-by-step explanation:
The entropy change (ΔS) for a chemical reaction can be positive, negative, or zero, indicating an increase, decrease, or no change in disorder, respectively.
(b) 2Fe(s) + 3/2 O₂ (g) → Fe₂O₃ (s): ΔS is likely negative because there's a decrease in the number of gaseous molecules, which decreases entropy.
(c) 2C6H14(l) + 19O₂(g) → 14H₂O(g) + 12CO₂(g): ΔS is positive. Even though the number of gas molecules increases, which usually increases entropy, predicting ΔS just based on molecule count can be challenging.
For the combustion of methane, CH4(g) + 2O₂(g) → CO₂(g) + 2H₂O(g), predicting whether ΔS is positive or negative is difficult because both the reactants and products are gases, and the reaction involves both the breaking and forming of chemical bonds.