[science123]

Given the following data,

H2(g) + 1/2 O2(g) => H2O(g) DGo = -236.0

2 H(g) + O(g) => H2O(g) DGo = -920.8

2 H(g) + 2 O(g) => H2O2(g) DGo = -1,068.0

2 O(g) => O2(g) DGo = -496.6

H2O2(l) => H2O2(g) DGo = 43.1

Determine DGfo for H2O2(l)

Correct : -178.0

I don't know which equations to combine and flip and how do we find the Gf of H2O2 (gas) . I was thinking of someway to find gf of H2O2 gas and subract from Grxn to get Gf of H2O2 liquid. Thanks!

[sjb]

What's the definition of  :delta: Gf?

[science123]

What's the definition of  :delta: Gf?

Change of Gibbs free energy that accompanies the formation of 1 mole of that substance from it's elements in standard state.

[sjb]

What's the definition of  :delta: Gf?

Change of Gibbs free energy that accompanies the formation of 1 mole of that substance from it's elements in standard state.

Right, so what does that mean, in terms of your reaction?

[science123]

Delta Go = sum of Delta Gf of products - sum of Delta Gf of reactants
Am i right?

[sjb]

Essentially, yes. You're after  :delta: Gf for H₂O₂(l), which is for the reaction H₂(g) + O₂(g)  H₂O₂(l). Can you find a path using the data you have that allows you to calculate this  H₂(g) + O₂(g) A  B  C ...  H₂O₂(l)?

[science123]

That's that part i am not getting. And btw why does eq. 2 has hydrogen in atomic form?

[sjb]

You won't necessarily have to use them all (I've not worked it through, so could be wrong here).

For instance, from

H₂(g) + 1/2 O₂(g)  H₂O(g)  :delta: Go = -236.0

2 H(g) + O(g)  H₂O(g)  :delta: Go = -920.8

H₂(g) + 1/2 O₂(g)  H₂O(g)  2 H(g) + O(g)

you can calculate  :delta: Gf for 2 H(g) + O(g), by adding equation 1 to the reverse of equation 2; giving 684.8. (Don't forget your units!)