Combustion reaction occurs when organic compound reacts with oxygen to form CO₂, H₂O and energy C(s) + O₂(g) → CO₂(g) is Synthesis reaction not combustion 2 H₂(g) + O₂(g) → 2 H₂O(g) also Synthesis reaction and not combustion C₃H₈(g) + 5 O₂ → 3 CO₂(g) + 4 H₂O(g) is considered as Combustion reaction 2 C₃H₇OH(l) + 9 O₂(g) → 6 CO₂(g) + 8 H₂O(g) Combustion reaction