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An ionic compound has a solubility of $1\ \mathrm M$ in water at $25\ ^\circ \mathrm C$ and its solubility increases as the temperature is raised. What are the signs of $\Delta H^\circ$ and $\Delta S^\circ$ for the dissolving process?

Since the the solubility increases as the temperature is raised ($\Delta G^\circ$ becomes more negative), I know that $\Delta S^\circ$ is positive. However, I am unsure of how to determine the sign of $\Delta H^\circ$. The answer is $\Delta H^\circ > 0$.

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    $\begingroup$ Hint: What happens to the bonds in the substance as it dissolves... $\endgroup$ – Night Writer Jan 20 at 20:06
  • $\begingroup$ I know the bonds break (delta H is positive), but I thought that some substances, like NaOH, dissolve exothermically (so delta H is negative)? $\endgroup$ – DrPepper Jan 20 at 23:38
  • $\begingroup$ I am not sure the proposer of the exercise want all this but your doubt is legitimate. See here: chemistry.stackexchange.com/questions/51862/… $\endgroup$ – Alchimista Jan 21 at 10:09
  • $\begingroup$ See answer about Van't Hoff equation here. $\endgroup$ – Karsten Theis Jan 21 at 15:02
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    $\begingroup$ The statement about $\Delta G^\circ$ is not quite true. K becomes larger, and $\frac{\Delta G^\circ}{T}$ becomes more negative as the temperature increases. $\endgroup$ – Karsten Theis Jan 21 at 15:17

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