The balanced equation for the reaction of phosphorus with oxygen gas depends on the conditions of the reaction, which determine the product formed. Here are the two main possibilities:

1. Reaction to form phosphorus(III) oxide (P₄O₆):

This reaction occurs when phosphorus is burned in a limited supply of oxygen.

P₄(s) + 3O₂(g) → P₄O₆(s)

2. Reaction to form phosphorus(V) oxide (P₄O₁₀):

This reaction occurs when phosphorus is burned in an excess of oxygen.

P₄(s) + 5O₂(g) → P₄O₁₀(s)

Both equations are balanced, meaning that the number of atoms of each element is the same on both sides of the equation.