Question

The oxidation of glucose to carbon dioxide and water is represented by the following reaction, whether the oxidation occurs by combustion in the laboratory or by biological oxidation in living cells:

C6H12O6+6O2⇌6CO2+6H2O
When combustion is carried out under controlled conditions in the laboratory, the reaction is highly exothermic, with an enthalpy change (ΔH) of −673kcal/mol. As you know, ΔG for this reaction at 25∘C is −686kcal/mol, so the reaction is also highly exergonic.Without doing any calculations, would you expect ΔS (entropy change) for this reaction to be positive or negative? Explain your answer. A) ΔS would be positive because the reaction releases energy, increasing disorder in the system.
B) ΔS would be negative because the reaction is highly exothermic.
C) ΔS would be positive because the reaction is spontaneous.
D) ΔS would be negative because the reaction involves combustion.
E) ΔS would be zero because the reaction is highly exergonic.

Answer 1

The entropy change (ΔS) for the oxidation of glucose is positive, mainly due to the increase in number and mass of gaseous molecules, indicating increased disorder in the system.

Step-by-step explanation:

The expected entropy change (ΔS) for the oxidation of glucose to carbon dioxide and water would be positive. This is because the reaction results in an increase in the number of gaseous molecules, going from 6 molecules of O₂ to 12 molecules (6 CO₂ + 6 H₂O) in the products. According to Figure 14.3.6, the positive entropy change is due mainly to the greater mass of CO₂ molecules compared to those of O₂, which suggests a dispersal of energy and increased randomness or disorder in the system. The fact that the reaction is spontaneous and exothermic (as shown by the negative ΔG and ΔH values) also typically correlates with a positive entropy change. Therefore, option C) is the correct answer. It is important to note that heat release, in itself, is not a direct indicator of entropy change; the key factor is the increase in disorder, mainly manifested by the increased number of gas particles.