Ca(OH)2 dissolves exothermically in water and the molar solubility of Ca(OH)2 decreases as the temperature increases. What are the signs of delta H and delta S for dissolving Ca(OH)2?
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Use dG = dH - TdS. You know dH is negative. What must dS be to give dG - at low T and + at high T.
To determine the signs of ΔH (enthalpy change) and ΔS (entropy change) for the dissolution of Ca(OH)2, we need to consider the given information.
Given that the dissolution of Ca(OH)2 is exothermic, this means that heat is released when the compound dissolves in water. Exothermic reactions have a negative value for ΔH.
The information also states that the molar solubility of Ca(OH)2 decreases as the temperature increases. This implies that, at higher temperatures, fewer moles of Ca(OH)2 dissolve per liter of water, which indicates a decrease in entropy. Therefore, the dissolution process is associated with a decrease in disorder, resulting in a negative value for ΔS.
To summarize:
- ΔH is negative (exothermic process)
- ΔS is negative (decrease in disorder)
Overall, the dissolution of Ca(OH)2 is a spontaneous process as the negative ΔG (free energy change) enhances the solubility of the compound in water.