When two or more substances chemically bonded together to produce a single product, it is called a combination reaction or synthesis reaction.
Formation of calcium oxide by the combination elements of calcium and oxygen.
2Ca + O2 → 2CaO
Formation of ammonia by the combination of elements nitrogen and hydrogen.
N2 + 3H2 → 2NH3
Reaction of calcium oxide in water to form calcium hydroxide
CaO + H2O → Ca(OH)2
Formation of sulphur trioxide by the combination of sulphur dioxide and oxygen.
2SO2 + O2 → 2SO3
