In a combination reaction the atoms and/or molecules do what the name implies: they combine to form the product. Combination reactions are always exothermic. For example barium metal and fluorine gas will combine in a highly exothermic reaction to form the salt barium fluoride:  Another example is given by magnesium oxide combining with carbon dioxide:  Often, reaction can fall into more than one category. For example the combustion of magnesium metal is also a combination reaction:  |
