Is heat always released during a chemical reaction?
No, heat is not always released during a chemical reaction.
Exothermic reactions are ones where heat is released. The combination of water and calcium chloride is exothermic, because heat is released.
However, other types of reactions, called endothermic reactions, can also occur. Endothermic reactions are those where heat is taken in. For instance, the reaction of barium hydroxide octahydrate crystals with dry ammonium chloride is endothermic, because heat is taken in.
Almost all reactions are classified into the two groups, endothermic and exothermic.