## 1. Overall Reaction $\ce{ 2H_2 + O_2 -> 2H_2O}$ Modeling it might involve as many as 40 reactions involving 8 species ($H_2$, $O_2$, $H_2O$, $OH$, $H$, $O$, $HO_2$ and $H_2O_2$) ## 2. Initiation At all temperatures $\ce{H_2 + O_2 -> HO_2 + H\tag{chain initiation}}$ Only at high temperatures $\ce{H_2 + M -> H + H + M\tag{chain initiation}}$ ## 3. Propagation $\ce{H + O_2 -> OH + O\tag{chain branching}}$ this is endothermic and wont proceed rapidly at low temperatures $\ce{O + H_2 -> OH + H\tag{chain branching}}$ $\ce{OH + H_2 -> H_2O + H\tag{chain propagating}}$ $\ce{O + H_2O -> OH + OH\tag{chain propagating}}$ ## 4. Termination $\ce{H + H + M -> H_2 + M\tag{chain termination}}$ $\ce{O + O + M -> O_2 + M\tag{chain termination}}$ $\ce{H + O + M -> OH + M\tag{chain termination}}$ $\ce{H + OH + M -> H_2O + M\tag{chain termination}}$ At higher temperatures tertiary reactions involving $HO_2$ and $H_2O_2$ become important