Hi- Please provide a detailed explanation for each choice. The answer is positiv

Question

Hi- Please provide a detailed explanation for each choice. The answer is positive, positive. Why is that and how can you tell? I did post this question previously, but no explanation was given. I thought that delta H would be negative because the T is less than the original, so that since it is releasing heat it would be exothermic. Also, with S why is it producing a positive S value? Please explain!! Thanks!!

When ammonium chloride dissolves in water the temperature of the solution is less than that of the original water sample. Thus, we know that H is ____________ and that S is __________.

negative, negative

positive, positive

negative, positive

positive, negative

negative, zero

Explanation / Answer

Ans. When ammonium chloride dissolves in water the temperature of the solution is less than that of the original water sample. Thus, we know that dH is Positive and that dS is Positive.

The enthalpy of solvation of NH4Cl is +14.7 kJ/mol. That is, when 1 mol NH4Cl is dissolved in sufficient amount of water, the solution (system) absorbs 14.7 kJ heat from the surrounding. By convention, the enthalpy change of the system is considered positive when it absorbs heat. Therefore, dH is positive.

NH4Cl molecules in the solid state has no freedom of movement. When dissolved in water, the molecules are free to randomly move through the aqueous phase. Therefore, NH4Cl in aqueous phase has higher entropy (degree of freedom) that that of in solid state. Therefore, solvation increases entropy of NH4Cl molecules. By convention, the increase in entropy is considered positive. Therefore, entropy change for solvation of NH4Cl is positive.

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