# Unknown hess cycleWatch

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#1
Need help with understanding this hess cycle as oxygen is not really taken into account; why is that? Also , what are the equations suggesting. I get that the elements will form 6CO2 AND 6H20 to make the products but there is not enough oxygen though...

Thanks
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3 years ago
#2
Have you drawn the cycle?
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#3
(Original post by alow)
Have you drawn the cycle?
I have but it's really messy. I just don't really understand it. I get that 6c will form 6 co2 meaning 6*-394 and 6H2 form 6H2O so 6*-286 . This is the reverse of -2801, which will now be 2801. But in order to form 6 co2 and 6 water, you need you have 21 o but there are only 6 in the equation, how does it work?? I am referring to 6c .
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3 years ago
#4
(Original post by coconut64)
I have but it's really messy. I just don't really understand it. I get that 6c will form 6 co2 meaning 6*-394 and 6H2 form 6H2O so 6*-286 . This is the reverse of -2801, which will now be 2801. But in order to form 6 co2 and 6 water, you need you have 21 o but there are only 6 in the equation, how does it work?? I am referring to 6c .
There's a mistake in the question. The formation of H2O should have 1/2 O2, not 1 1/2.

The numbers work out when you change that.
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#5
(Original post by alow)
There's a mistake in the question. The formation of H2O should have 1/2 O2, not 1 1/2.

The numbers work out when you change that.
What about the formation of CO2, which needs 12 oxygen?
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3 years ago
#6
(Original post by coconut64)
What about the formation of CO2, which needs 12 oxygen?
Have a look at the equation for the combustion of glucose. It has 12 extra O atoms in it.
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#7
(Original post by alow)
Have a look at the equation for the combustion of glucose. It has 12 extra O atoms in it.
This is the part I'm confused with.

This is how I interpret it: to form 6 co2 you need 12 oxygen + 6 oxygen to form 6 water. Altogether you need 18 oxygen as reactants but there is only 6 oxygen available as far as I can see in the original equation. Without enough oxygen, how is the reaction supposed to work to form carbon dioxide and water that will form C6H12O6??
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3 years ago
#8
(Original post by coconut64)
This is the part I'm confused with.

This is how I interpret it: to form 6 co2 you need 12 oxygen + 6 oxygen to form 6 water. Altogether you need 18 oxygen as reactants but there is only 6 oxygen available as far as I can see in the original equation. Without enough oxygen, how is the reaction supposed to work to form carbon dioxide and water that will form C6H12O6??
Are these two reactions equivalent?

6C + 6H2 + 3O2 ---> C6H12O6

6C + 6H2 + 9O2 ---> C6H12O6 + 6O2
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#9
(Original post by alow)
Are these two reactions equivalent?

6C + 6H2 + 3O2 ---> C6H12O6

6C + 6H2 + 9O2 ---> C6H12O6 + 6O2
I don't think so since the second one produces an extra product which is oxygen but other than that they are the same
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3 years ago
#10
(Original post by coconut64)
I don't think so since the second one produces an extra product which is oxygen but other than that they are the same
Does it? Is the first one not the second one just simplified (so therefore the enthalpy change will be the same)?
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#11
(Original post by alow)
Does it? Is the first one not the second one just simplified (so therefore the enthalpy change will be the same)?
I am really lost.... Can you explain what I'm actually trying to solve in this question?
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3 years ago
#12
(Original post by coconut64)
I am really lost.... Can you explain what I'm actually trying to solve in this question?
You're trying to draw a Hess cycle which can give you the enthalpy change of reaction 4.1.

Do you know how to draw a Hess cycle?
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#13
(Original post by alow)
You're trying to draw a Hess cycle which can give you the enthalpy change of reaction 4.1.

Do you know how to draw a Hess cycle?
I figured that the oxygen will eventually cancel out, thanks for your time
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3 years ago
#14
(Original post by coconut64)
I figured that the oxygen will eventually cancel out, thanks for your time
No problem
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