# Where does the energy in the exothermic reaction of CaCl2 with water come from?

Today I created $1~\mathrm{M}$ aqueous solution of $\ce{CaCl2}$ and realized that the water before the mixture had a temperature of 23.4 Celsius degrees. Then I added the $\ce{CaCl2}$ and the temperature started growing until it reached 27.5 Celsius degrees. So we have an exothermic reaction. What does that actually mean and how does it work in my example? By the book, an exothermic reaction occurs, when the energy stored in reactants is smaller than the energy stored in products.

Here we have (with my opinion):

$$\ce{CaCl2 + H2O <=> Ca^{2+} + 2Cl^{-} + H2O}$$

From where did that energy come from? Is it just released from the fission of $\ce{CaCl2}$ reactant or from the fusion of some molecules of $\ce{CaCl2}$ again in products? Also, is it possible to have in the products side $\ce{CaCl2}$ molecules or only ions of $\ce{Ca}$ and $\ce{Cl}$?