Endo and Exothermic Reactions

Well lets start out by first describing what each of these reactions are. An exothermic reaction is a chemical reaction in which heat is given off. An endothermic reaction would thus be the opposite, a chemical reaction in which heat is absorbed. Do not get this confused with endergonic reactions in which energy not heat is absorbed. Now that we know what each reaction is lets talk about some examples of each of these as it relates to the pastry world. Whenever you boil water you are producing an endothermic reaction. The evaporation of water moleculars provides this reaction. The melting of ice crystals also provides you with an endothermic reaction. Another great example of this would be photosynthesis. (The process in which sunlight provides energy to plants to convert carbon dioxide into organic compounds) Without this endothermic reaction we wouldn't have all that beautiful produce in which to make our delectable desserts. Lets switch gears and talk about exothermic reactions. Whenever you burn something you are essentially creating an exothermic reaction. So the next time you are toasting nuts spices etc. just think to yourself...wow what a cool exothermic reaction I am creating. Adding concentrated acid to water is also an exothermic reaction. One of my favorite examples would be the production of chocolate. To be even more specific molded chocolate bon bons. Whenever you temper chocolate and cast chocolate molds you are giving off heat (latent heat of crystallization) When chocolate is crystallizing the cocoa butter is actually changing from a liquid to a solid and in turn gives off heat. I was looking on youtube the other day and found a really interesting clip of "hot ice" using the chemical sodium acetate trihydrate. Basically this is a really dramatic exothermic reaction. Check out the link below to learn how to make "hot ice" (Not really related to pastry but still super cool) http://www.youtube.com/watch?v=aC-KOYQsIvU