A difficult concept for many students to understand is the energy involved in breaking and forming bonds. A hydrate is a substance that has water bonded to it. In order to dehydrate you must add energy (endothermic) to break the bond to water. When hydrating you are forming a bond to water and will release energy (exothermic). This visual demonstration reinforces the concept.
Copper (II) Sulfate Penta Hydate is heated and water is driven of (bonds broken)
Water is add (bonds form) heat is then released
Exothermic to make bonds
endothermic to break bonds