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Why is the enthalpy of solution of hydrated calcium chloride positive?
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Les McLean
Why is the enthalpy of solution of hydrated calcium chloride positive?
Dissolution enthalpy is kind of scale balancing as being combination of lattice energy ( positive solid matrix breaking enthalpy) and hydration enthalpy(usually negative), following the formal process
The hydration enthalpy is very negative for anhydrous $\ce{CaCl2}$, but just little negative for $\ce{CaCl2.6H2O}$. It leads to negative dissolution enthalpy for the former, but positive one for the latter.
There is more of known $\ce{CaCl2}$ hydrates. Aside of the hexahydrate, the most common $\ce{CaCl2.2 H2O}$ has the dissolution enthalpy much closer to zero than for the above two cases.
Dissolution enthalpy is kind of scale balancing as being combination of lattice energy ( positive solid matrix breaking enthalpy) and hydration enthalpy(usually negative), following the formal process
The hydration enthalpy is very negative for anhydrous $\ce{CaCl2}$, but just little negative for $\ce{CaCl2.6H2O}$. It leads to negative dissolution enthalpy for the former, but positive one for the latter.
There is more of known $\ce{CaCl2}$ hydrates. Aside of the hexahydrate, the most common $\ce{CaCl2.2 H2O}$ has the dissolution enthalpy much closer to zero than for the above two cases.
Dissolution enthalpy is kind of scale balancing as being combination of lattice energy ( positive solid matrix breaking enthalpy) and hydration enthalpy(usually negative), following the formal process
$$\ce{CaCl2(s) -> Ca^2+(g) + 2 Cl-(g) ->[H2O] Ca^2+(aq) + 2 Cl-(aq)}$$
The hydration enthalpy is very negative for anhydrous $\ce{CaCl2}$, but just little negative for $\ce{CaCl2.6H2O}$. It leads to negative dissolution enthalpy for the former, but positive one for the latter.
There is more of known $\ce{CaCl2}$ hydrates. Aside of the hexahydrate, the most common $\ce{CaCl2.2 H2O}$ has the dissolution enthalpy much closer to zero than for the above two cases.
For more, see Wikipedia.org: Enthalpy change of solution
Dissolution enthalpy is kind of scale balancing as being combination of lattice energy ( positive solid matrix breaking enthalpy) and hydration enthalpy(usually negative), following the formal process
$$\ce{CaCl2(s) -> Ca^2+(g) + 2 Cl-(g) ->[H2O] Ca^2+(aq) + 2 Cl-(aq)}$$
The hydration enthalpy is very negative for anhydrous $\ce{CaCl2}$, but just little negative for $\ce{CaCl2.6H2O}$. It leads to negative dissolution enthalpy for the former, but positive one for the latter.
There is more of known $\ce{CaCl2}$ hydrates. Aside of the hexahydrate, the most common $\ce{CaCl2.2 H2O}$ has the dissolution enthalpy much closer to zero than for the above two cases.
For more, see Wikipedia.org: Enthalpy change of solution
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