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# Hess's Law

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1. Hi,

I am slightly confused with this and was wondering if anyone could help.

So there are no numbers I need to input yet, I am just trying to understand the process:

2C + 3H2 = C2H6 (formation)

∆H1 = 2CO2 and ∆H2 = H2o

What I don't get is why are we only using Carbon on one side and Hydrogen on the other?

The other problem I really don't get...

2C + 3H2 + 1/2 O2 = C2H5OH

∆H1 = 2CO2 and ∆H2 = 3H2O

Why 3 moles of hydrogen? There isn't 3 moles of hydrogen in the products?

Sorry for sounding thick? Any help is greatly appreciated
2. (Original post by Lambert87)
Hi,

I am slightly confused with this and was wondering if anyone could help.

So there are no numbers I need to input yet, I am just trying to understand the process:

2C + 3H2 = C2H6 (formation)

∆H1 = 2CO2 and ∆H2 = H2o

What I don't get is why are we only using Carbon on one side and Hydrogen on the other?

The other problem I really don't get...

2C + 3H2 + 1/2 O2 = C2H5OH

∆H1 = 2CO2 and ∆H2 = 3H2O

Why 3 moles of hydrogen? There isn't 3 moles of hydrogen in the products?

Sorry for sounding thick? Any help is greatly appreciated
It looks like you are using formation enthalpy to work out other enthalpy changes, but it's not very clear.

Check out this interactive on Hess' law for a full explanation.

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