Thermodynamics and Equilbrium 2. Would 25°C be considered a high temperature or

Question

Thermodynamics and Equilbrium 2. Would 25°C be considered a high temperature or a low temperature for the following reaction? 90.3 AH,,J/mol 33.2 S,J/mol K 239.9 ?G, , kj/mol -173.2 155.6 -285.8 210.7 86.6 69.9 51.0-237.2-79.9 a. Is this reaction exothermic or endothermic? Explain your answer b. Docs this reaction have an increase or a decrease in entropy? Explain your answer in two different ways c. Is this reaction spontaneous or nonspontancous at 25°C? Explain your answer d. Explain how you use this information to answer the original question.

Explanation / Answer

2. a) Change in reaction enthalpy:

Sum of enthalpies of products - sum of enthalpies of reactants= [2×(-173.2)+(+90.3)] - [(-285.8)+(+33.2)] kj = -3.5 kj

As enthalpy change of the reaction is negative; it is an exothermic reaction.

(b)

Chnage in entropy = Sum of entropies of products - Sum of entropies of reactants = [2×135.6+210.7]-[3×239.9+69.9] j/ k = -307.7 j/k=-0.3077 kj/K

There is decrease in entropy.

(c)

Change in Gibbs free energy = [2×(-79.9)+86.6]- [3×51-(-237. 7)] kj = 11.5 kj

Since Gibbs free energy change is positive at 25 C; the reaction is not spontaneous.

(d)

We know : delG = delH-T×delS=-3.5 -T×(-0.3077) = -3.5 +0.3077×T

The reaction is spontaneous if delG is negative.To keep delG negative 3.5 should be greater than T×0.3077. It is possible if T (temperature) is very low.

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