What can be said about an endothermic reaction with a negative entropy change in terms of spontaneity?

• A. The reaction is nonspontaneous at all temperatures.
• B. The reaction is spontaneous at low temperatures.
• C. The reaction is spontaneous at all temperatures.
• D. The reaction is spontaneous at high temperatures.

Answer: (A)

Verified step by step guidance

1. Understand the concepts: An endothermic reaction absorbs heat, meaning the change in enthalpy (ΔH) is positive. A negative entropy change (ΔS) indicates a decrease in disorder.
2. Recall the Gibbs free energy equation: ΔG = ΔH - TΔS, where ΔG is the change in free energy, ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.
3. Determine spontaneity: A reaction is spontaneous if ΔG is negative. For an endothermic reaction (ΔH > 0) with a negative entropy change (ΔS < 0), both terms in the Gibbs free energy equation contribute positively to ΔG.
4. Analyze temperature effects: Since both ΔH and -TΔS are positive, increasing temperature (T) will increase the positive contribution of -TΔS, making ΔG more positive, thus less likely to be spontaneous.
5. Conclude the spontaneity: Given that both ΔH and -TΔS are positive, the reaction is nonspontaneous at all temperatures because ΔG will always be positive.