What can you say about the free energy and entropy of this reaction?

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A pair of students found the temperature of 100. g of water to be 26.6 C. They then dissolved 8.47 g of KCL in the water. When the salt had dissolved, the temperature of the water was 21.9 C

What can you say about the free energy and entropy of this reaction?
— it is spontaneous right? what else… help

Best reply by hfshaw:

The question says the salt dissolved, so the reaction:

KCl(s) -> K+(aq) + Cl-(aq)

is spontaneous.

The Gibbs free energy change for a spontaneous reaction is negative, so ΔG for the above reaction is < 0. The temperature of the system decreased when the KCl dissolved, That means that the reaction is endothermic, so ΔH for the reaction is > 0.

You should know that ΔG = ΔH – T*ΔS, and we already established that ΔG < 0 and ΔH > 0 for this reaction. This implies that T*ΔS > ΔH, so ΔS > 0 for this reaction (because T is measured in kelvins, and is always > 0).

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What can you say about the free energy and entropy of this reaction?

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