What are the balanced thermochemical equations for the dissolving of calcium chloride In water?
Answer 1:
Start by writing out your reactants: \(\mathrm{CaCl}_{2}+\mathrm{H}_{2} \mathrm{O}.\) We now need to determine what kind of reaction this is. Is it a…
Synthesis reaction? No, you can’t have \(\mathrm{CaCl}_{2} \mathrm{H}_{2} \mathrm{O}\) since we’re not dealing with polyatomic ions.
Decomposition reaction? No, there are two reactants.
Combustion reaction? No, there’s no carbon.
Single replacement? No, there are not 3 elements in total.
Double replacement? Seems like it; there are 4 elements making up two compounds.
We now predict products: \(\mathrm{CaCl}_{2}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{CaO}+\mathrm{HCl}\). Now balance: \(\mathrm{CaCl}_{2}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{CaO}+2 \mathrm{HCl} .\) Since \(\mathrm{CaO}\) is a solid, our reaction works. Hopefully this is what you’re asking for, shoot me a PM if not.
Answer 2:
\(\text{Warning! Long Answer.}\) The balanced equation is
\(\mathrm{CaCl}_{2}(\mathrm{~s}) \stackrel{\mathrm{H}_{2} \mathrm{O}}{\longrightarrow} \mathrm{Ca}^{2+}(\mathrm{aq})+2 \mathrm{Cl}^{-}(\mathrm{aq})\)
There are three steps in the process of dissolving \(\mathrm{CaCl}_{2},\)
Step 1. The ions must separate from each other
\(\mathrm{CaCl}_{2}(\mathrm{~s}) \rightarrow \mathrm{Ca}^{2+}+2 \mathrm{Cl}^{-} ; \Delta H_{2}\)It takes energy to separate the ions from each other, so this step is \(\text{endothermic.}\) \(\Delta H_{2}>0\)
Step 2. The water molecules must separate from each other to make room for the ions
It takes energy to separate the water molecules from each other, so this step is also \(\text{endothermic.}\) \(\Delta H_{1}>0\)
Step 3. The ions interact with the water molecules and form hydrated ions.
Some of the water becomes water of hydration.
\(\mathrm{Ca}^{2+}+2 \mathrm{Cl}^{-}+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \stackrel{\mathrm{H}_{2} \mathrm{O}}{\longrightarrow} \mathrm{Ca}^{2+}(\mathrm{aq})+2 \mathrm{Cl}^{-}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{hyd}) ; \Delta H_{3}\) This step is \(\text{endothermic.}\) So \(\Delta H_{3}>0\)
The overall process
The overall process is the sum of the three steps.
When calcium chloride dissolves, the energy released by hydrating the ions \(\left(\Delta H_{3}\right)\) is greater than the energy required to separate the ions and the water molecules \(\left(\Delta H_{1}+\Delta H_{2}\right).\)
Thus, the dissolving of calcium chloride in water is an \(\text{exothermic}\) process, and the heat evolved goes into heating the solution in the heating pack
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