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# Hess's Law and Enthalpy Change

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1. [attach]5.4402954403154405e+23[/attach]
Why is my cycle wrong? The answer doesn't match if I use this cycle.
Thanks for any help in advance!
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2. (Original post by 123PC)

[attach]5.4402954403154405e+23[/attach]
Why is my cycle wrong? The answer doesn't match if I use this cycle.
Thanks for any help in advance!
I can't make head or tail out of your "cycle".

The question is much easier than this. Simply construct the equation you need by manipulating the equations given.

Multiply equation 2 by 3
Reverse equation 1
3. (Original post by charco)
I can't make head or tail out of your "cycle".

The question is much easier than this. Simply construct the equation you need by manipulating the equations given.

Multiply equation 2 by 3
Reverse equation 1
So I get:
3C + 3/2 O2 ---> 3CO2 enthalpy change: -110*3
Fe2O3 ----> 2Fe + 3/2O2 enthalpy change: +882
3C + Fe2O3 + 3/2 O2 ----> 3CO2 + 2Fe + 3/2 O2
or, 3C + Fe2O3----> 3CO2 + 2Fe enthalphy change: -330+882=+552
Where did I go wrong here?
4. (Original post by 123PC)
So I get:
3C + 3/2 O2 ---> 3CO2 enthalpy change: -110*3
Fe2O3 ----> 2Fe + 3/2O2 enthalpy change: +882
3C + Fe2O3 + 3/2 O2 ----> 3CO2 + 2Fe + 3/2 O2
or, 3C + Fe2O3----> 3CO2 + 2Fe enthalphy change: -330+882=+552
Where did I go wrong here?
pressing the buttons on the calculator ...

-330 + 822 = +492
5. (Original post by charco)
pressing the buttons on the calculator ...

-330 + 822 = +492
Whoops, sorry, thanks!

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