triangle"H^of△Hof = triangle"H of products"△H of products - triangle"H"^of "reactants"△Hofreactants
triangle"H^of△Hof = triangle"H^of H_2O△HofH2O - triangle"H^of H_2△HofH2 - triangle"H^of O_2△HofO2
triangle"H^of△Hof = -280KJ - 0 + 0
= -280KJ
The difference between triangle"H^of△Hof and triangle"H of reaction"△H of reaction in this reaction is that triangle"H^of△Hof doesn't rely on the real reaction like here actually gaseous water is formed.
We have to calculate triangle"H of reaction"△H of reaction
For example
"Bond energies of reactant - (Bond energies of product)"Bond energies of reactant - (Bond energies of product)
To calculate heat of formation we need a reaction that only forms water
2H_2 + O_2 = 2H_2O2H2+O2=2H2O
[Bond energy of product that is H_2OH2O]
Bond energy of H_2O H2O
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Bond energy of O-H = 463KJ
No. of O-H bonds in water = 2
Bond energy of H_2OH2O = 463KJ * 2 = 926KJ
There are 2 moles of water formed so bond energy will be twice
926KJ * 2 = 1852KJ
[Bond energy of products that is O_2O2 and H_2OH2O]
Lewis dot structure of oxygen
![wikihow]()
Bonds found in oxygen is 1 oxygen double bond
O = O = 499KJ
Lewis structure of Hydrogen
![scientifictutor]()
Bonds found in hydrogen is 1 H-H bond
H-H = 436KJ
There are 2 moles of hydrogen so the bond energy would be twice
436KJ * 2 = 872KJ
"Bond energy of oxygen + Bond energy of hydrogen - (Bond energy of water)"Bond energy of oxygen + Bond energy of hydrogen - (Bond energy of water)
"triangleH" = (872KJ + 499KJ) - 1852KJ = -481KJ triangleH=(872KJ+499KJ)−1852KJ=−481KJ
For the reaction
H_2+ 1/2O_2 = H_2O H2+12O2=H2O
the triangle H "of formation"△Hof formation would be of 1/212 value = -240.1KJ
because all the products have become halve
