Why is the maximum adiabatic temperature found for an equivalence ratio a bit higher than 1?

Why does the peak adiabatic temperature usually happen for an equivalence ratio a bit higher than 1? I think it had something to do with the probability of each fuel molecule finding a corresponding oxidizer, and the fact that the molecular weight of the fuel is generally higher than that of the oxidizer. 


![](https://i.stack.imgur.com/CP7qK.png)




I actually found the answer in this [2011 paper](https://web.archive.org/web/20121229075337/http://lcg.princeton.edu:80/publications/conference-publications/law-on-the-off-stoichiometric-peaking-of-adiabatic-flame-temperature.aspx), here is a quote from the abstract:



> 
> The characteristic rich shifting of the maximum adiabatic flame temperature from the stoichiometric value for
>  hydrocarbon/air mixtures is demonstrated to be caused by product dissociation and hence reduced amount of heat release.
>  Since the extent of dissociation is greater on the lean side as a result of the stoichiometry of dissociated products, the peaking
>  occurs on the rich side.
> 
> 
> 


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