[Toxage]

 Calculate, using the table of average bond energies (reverse side):

Helpful Information In Kcal/mole:

Average Bond Energies:

H-H 104.2

O-O 118.3 (O2 Molecule)

O-O 33.2 (H2O2 Molecule)

H-O 110.6

Enthalpies Of Formation In kcal/mole:

H2O (g) -57.8




1. H2O (G) (Ans -57.9 kcal) My teacher tells us the correct answer, and then we must show the work. My work is way off. 

My Work:

4H2 + O2 -----> 2H20

Break Bonds:
4 Mole H-H Bonds 4*104.2= 416.8
2 Mole O-O Bonds 2*118.3= 236.6

Create Bonds:
4 H-O Bonds 4*110.6=-442.4

+653.4
-442.4

Heat Of Formation= +211 kcal/mole.

[enahs]

First, balance the equation properly. When you balance it, how many mols of water are you forming?

[Toxage]

I don't understand what you mean balance it properly?

I am forming H2O.

H+O-->H2O

But H and O are both diatomic...

So H2 + O2 --> H2O

But H is double that of water so I need to re-balance it.

2H2 + O2 ---> H2O

Product side not equal

2H2 + O2 ---> 2H2O

I don't understand how it isn't balanced.

[enahs]

Because that equation has different coefficients then the original one you posted. And in the original one you posted, in your calculations, you multiplied by those other wrong coefficients.

[Toxage]

What I don't understand. What is the correct balanced equation?

[enahs]

The second one you posted is correct.

See the difference in the two?

[Toxage]

What second one ? I have no clue what equation your referring to can you copy the one that is right? Are you referring to the H2 + O2 --> H2O? Because that seems wrong because an O is missing on the product side.

[enahs]

The one in your second post in this thread.

I.E., look at your first post and question, then compare it to the second post (by you).

Calculate it with the equation from your second post.

2H2 + O2 -> 2H2O

I think you are making this much more complicated then it is.

[Toxage]

The one in your second post in this thread.

I.E., look at your first post and question, then compare it to the second post (by you).

Calculate it with the equation from your second post.

2H2 + O2 -> 2H2O

I think you are making this much more complicated then it is.

What do you mean? This is extremely complicated no one can figure out how to do this problem.

I used 2H2 + O2 -> 2H2O but it still doesn't work for a final answer I get -115.7kcal/mol.


Break Bonds:
2 Mole H-H Bonds 2*104.2= 208.4
1 Mole O-O Bonds 1*118.3= 118.3

Create Bonds:
4 H-O Bonds 4*110.6=-442.4

+326.7
-442.4

Heat Of Formation= -115.7.

[Padfoot]

Heat Of Formation= -115.7 kcal/mole.

Your value relates to 2 mol of H₂0, not 1.