Question

Bond Enthalpies

Answer 1

Formula is \[2H_2+O_2->2H_2O\]

Answer 2

\[\Delta~H= -572 kJ\]

Answer 3

Calculate the average bond energy in a H-H bond.

Answer 4

So the formula is \[\Delta~H=\Sigma~BE_(bonds~broken)-~\Sigma~BE_(bonds~formed)\]

Answer 5

O=O - 195 kJ/mol
O-H- 467 kJ/mol

Answer 6

How would this work? I attempted solving for x but I got a whacky number.

Answer 7

@Tranquility do you think you can help me with this?

Answer 8

Which bonds are broken?
Which bonds are formed?

Hint:
Are the bonds on the reactants side broken or formed?
Are the bonds on the products side broken or formed?

Answer 9

I already know that the bonds broken are the diatomic hydrogen and oxygen, and the formed is the water. I just don't know how to continue x.x

Answer 10

Good! We also need to keep in mind the number of moles and we need to do the sum.

How many H-H bonds are broken?
How many O-O bonds are broken?

How many O-H bonds are formed?

Answer 11

Oh I see, so 2 moles of bonds are broken, 1 mole, and 2 moles.

Answer 12

Also, an important step that I forgot to check was to make sure your reaction is balanced. And in the question it is so we're fine

Answer 13

Well only 2 H-H bonds are being broken but we need to keep that coefficient in mind because it's not 1 mole of H2 but rather 2 moles. That tells us there are two bonds to be broken.

Answer 14

The only value which we don't know is the H-H enthalphy, however we know \(\Delta\)H so that's what we're trying to calculate.


Set it up

Answer 15

I wrote it down because it took much more effort to type it in than to do the actual problem haha. I got 401 kJ/mol, but I don't think that's right...

Answer 16

(Bonds broken) - (Bonds formed) = \(\Delta \)H

We agree that 2 H-H bonds are formed, the values which we do not know. So let's call it x kJ/mol
We have two moles so 2 * x
One O=O bond is broken. 195 kJ/mol
You might want to check that value though.
1 mole * 195kJ/mol = 195 kJ

2 O-H bonds are formed in 1 water molecule. However, we have 2 molecules of water, and therefore we have 4 O-H bonds formed.
4 moles * 467 kJ/mole = 1868 kJ

(2x + 195) - (1868 kJ) = -572 kJ

Solve for x

Answer 17

\(\color{#0cbb34}{\text{Originally Posted by}}\) @lowkey
O=O - 195 kJ/mol
O-H- 467 kJ/mol
\(\color{#0cbb34}{\text{End of Quote}}\)
I used this lmao, are these values wrong?

Answer 18

Is that what they gave you?

https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Chemical_Bonding/Fundamentals_of_Chemical_Bonding/Bond_Energies

O=O 495

So either it was a typo or they're making up numbers. But they used O-H as 467 which matches the literature value.

Answer 19

Huh. Well either way, you explained it very nicely, thank you so much!

Answer 20

No problem!