Thus the reaction is a good example of an endothermic reaction. The amount of heat given out or absorbed in a chemical reaction is called the heat of reaction . There is another definition that comes into use while discussing chemical reactions. This is heat of formation . The heat of formation is a little different from of heat of reaction.
Heat of formation comes into picture when the basic compounds or molecules are forming.
The amount of heat given out or absorbed when one mole of the constituent atoms is reacting to form 1 mole of the molecule, is called the heat of formation. The following examples will show how to calculate heat of formation of a compound. This is the heat of formation of water molecule. Let us calculate the heat of formation for NaCl. Besides bond breaking, Na atoms will also give off their excess electron.