Answer:
4 HBr + O2 → + 2H2O + 2Br2
Explanation:
Based on the following reaction mechanism:
HBr + O2 → HOOBr (slow)
HOOBr + HBr → 2HOBr (fast)
HOBr + HBr → H2O + Br2 (fast)
The equation for the overall reaction is the sum of the three reactions in which intermediaries of reaction (HOBr and HOOBr are canceled). That is 1 + 2 + 2*(3):
HBr + O2 + HOOBr + HBr + 2HOBr + 2HBr → HOOBr + 2HOBr + 2H2O + 2Br2
Beeing this reaction the equation of the overall reaction.