The balanced chemical equation :
P₄+3O₂⇒P₄O₆
A compound consists of the mole ratio of the constituent components
12.4 g of phosphorus, mol :
[tex]\tt mol=\dfrac{mass}{MW}\\\\mol=\dfrac{12.4}{31}\\\\mol=0.4[/tex]
9.6 g of oxygen, mol :
[tex]\tt mol=\dfrac{mass}{MW}\\\\mol=\dfrac{9.6}{16}\\\\mol=0.6[/tex]
the mole ratio of the compound resulting from the reaction of phosphorus and oxygen :
P : O = 0.4 : 0.6⇒ 4 : 6
The compound formula :
P₄O₆
So the reaction (balanced) :
[tex]\tt 4P+3O_2\rightarrow = P_4O_6[/tex]
Usually this reaction occurs when phosphorus reacts with a small amount of oxygen instead of excess oxygen(for excess oxygen, the compound produced :P₄O₁₀)