This is a best example to share when we talk about chemical change, that the products have totally different properties from that of the reactants , from which they are made.
Now coming to the answer,
Formation of water is a highly exothermic type of reaction and a lot of energy is lost at the time of reaction and the bond formed is having very less energy. And thus it can not yield more energy on combustion.
Like this:
Like Loading...
Related
Published by ankushmaster
I am M.Sc (chemistry ) from punjabi university.
I am a science teacher with expertise in chemistry, with 8 years of experiance in teaching. i am getting a handsome salary , now i wish to help out the people who need me UNCONDITIONALLY.
and I am constantly working on creating a new and easy way of learning the tough things in an effective way. I am constantly working to make authentic and reliable information to be shared with my students and widen the horizons of knowledge.
View all posts by ankushmaster
By 
The Unconditional Guru 