clhs sciblog

 The formation of bonds between atoms or molecules means sharing electrons between the composite atoms, and this can transform one substance into another; such as the synthesis of water (H₂O) from two gases: hydrogen (H₂) and oxygen (O₂). Some chemical interactions require energy: the substances must be mixed and heated for a chemical reaction to occur. These energy requiring reactions are called endothermic reactions. Whereas other chemical reactions release heat, and those energy releasing reactions are called exothermic reactions. On a molecular level, reactions can also be initiated by the addition or removal of electrons using electromagnetic radiation