At what temperatures is a reaction that has a positive change in entropy spontaneous?A.At lower temperatures for endothermic reactionsB.At no temperatures for exothermic reactionsC.At all temperatures for exothermic reactionsD.At all temperatures for endothermic reactions
Question
At what temperatures is a reaction that has a positive change in entropy spontaneous?A.At lower temperatures for endothermic reactionsB.At no temperatures for exothermic reactionsC.At all temperatures for exothermic reactionsD.At all temperatures for endothermic reactions
Solution
The spontaneity of a reaction is determined by the sign of the change in Gibbs free energy (ΔG). The equation for ΔG is ΔG = ΔH - TΔS, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.
If a reaction has a positive change in entropy (ΔS > 0), it means the reaction becomes more disordered as it proceeds.
A. At lower temperatures for endothermic reactions: This is not necessarily true. For an endothermic reaction (ΔH > 0), the reaction may or may not be spontaneous at lower temperatures. It depends on the magnitude of ΔS. If TΔS > ΔH, the reaction is spontaneous. If TΔS < ΔH, the reaction is not spontaneous.
B. At no temperatures for exothermic reactions: This is not necessarily true. For an exothermic reaction (ΔH < 0), the reaction can be spontaneous at any temperature if ΔS is positive enough to make ΔG negative.
C. At all temperatures for exothermic reactions: This is true. For an exothermic reaction (ΔH < 0), if ΔS is positive, then ΔG will always be negative (since T is always positive), and the reaction will be spontaneous at all temperatures.
D. At all temperatures for endothermic reactions: This is not necessarily true. For an endothermic reaction (ΔH > 0), the reaction may or may not be spontaneous at all temperatures. It depends on the magnitude of ΔS. If TΔS > ΔH at all temperatures, the reaction is spontaneous. If TΔS < ΔH at any temperature, the reaction is not spontaneous.
So, the correct answer is C. At all temperatures for exothermic reactions.
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