# Why doesn't oxygen replace chlorine?

If oxygen is more electronegative why doesn't it replace chlorine in compounds?

Example:

$\ce{2NaBr + Cl2 -> 2NaCl + Br2}$

works, while

$\ce{4NaCl + O2 -> 2Na2O + 2Cl2}$

doesn't.

With sodium chloride the pure sodium oxide is a strong base. As such it extracts a $\ce{Cl^+}$ moiety from any poyential chlorine molecules. Instead of the element, chlorine gets oxidized to oxyanions such hypochlorite (i.e., oxide coordinated to chlorine).
• Re: "chlorine gets oxidized to oxyanions such hypochlorite" So, the products formed from $\ce{Na2O\+Cl2}$ are $\ce{NaCl\+NaOCl}$? Thanks! – Gaurang Tandon Feb 13 '18 at 4:43
In order to know if a reaction is spontaneous or not (if it will happen towards the direction you have drawn it) you must look at its Gibbs energy, ΔG. Electronegativity of one element in a reaction is one of the many factors that contribute to it. In this case you are dealing with a redox reaction (because the oxidation states of the elements involved change) and therefore you need to use the relationship: ΔG=-nFE$^0$cell with E$^0$cell calculated from the relevant half reactions. For more details read an introduction to electrochemistry from some inorganic chemistry book.