Question

of spontaneity to deduce the signs . Use the observations about each chemical reaction in the table below to decide the sign (positive or negative) of the reaction enthalpy ΔΗ and reaction entropy AS This reaction is only below 146C

Answer 1

A.

The reaction is spontaneous at higher temperature means, endothermic reaction.

ΔH_rxn = positive and ΔS_rxn = negative

Consider initial conditions only, the reaction is spontaneous only above 7 ^oC, means initially non-spontaneous, endothermic, negative entropy.

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B.

The reverse reaction is always spontaneous because it is exothermic, but at lower temperature it becomes slow according to Lechatlier's principles. So initially

ΔH_rxn = negative and ΔS_rxn = positive

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C.

Crystallization is spontaneous only below 146 ^oC, means reaction is exothermic and we need to remove energy to make it possible.

ΔH_rxn = negative and ΔS_rxn = negative

crystallization process includes decrease in entropy.

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