Explanation:

A combination REACTION (also known as a synthesis reaction) is a reaction where two or more elements or compounds (reactants) combine to form a single compound (product). Such reactions may be represented by equations of the following form: X + Y → XY. The combination of two or more elements and form one compound is called combination reaction. Combination reactions can involve different types of reactants:

Type Example

a) Between elements C + O2 → CO2 Carbon completely BURNT in oxygen yields carbon dioxide

b) Between compounds CaO + H2O → Ca(OH)2 Calcium oxide (lime) COMBINED with water gives calcium HYDROXIDE (slaked lime)

c) Between elements and compounds 2CO + O2 → 2CO2 Oxygen combines with carbon monoxide, and carbon dioxide is formed.

There is no SPECIFIC number of reactants in a combination reaction.

Combination reactions are usually exothermic because when the bond forms between the reactants, heat is released. For example, barium metal and fluorine gas will combine in a highly exothermic reaction to form the salt barium fluoride: