If ΔH° is negative, what does this say about the favorability of a reaction?

• A. Reactants are favored.
• B. Products are favored.
• C. Neither side is favored.
• D. It depends on the temperature.

Answer: (D)

Verified step by step guidance

1. Understand that ΔH° represents the standard enthalpy change of a reaction, which is the heat absorbed or released under standard conditions.
2. Recognize that a negative ΔH° indicates an exothermic reaction, meaning heat is released to the surroundings.
3. Recall that exothermic reactions are generally more favorable because they release energy, making the products more stable than the reactants.
4. Consider the role of temperature in determining reaction favorability. While a negative ΔH° suggests product favorability, the overall favorability also depends on entropy (ΔS°) and temperature (T) as described by the Gibbs free energy equation: ΔG° = ΔH° - TΔS°.
5. Conclude that while a negative ΔH° suggests products are favored, the actual favorability of the reaction depends on the temperature and the entropy change, as these factors influence the Gibbs free energy (ΔG°), which ultimately determines spontaneity.