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# Enthalpy change of combustion Watch

1. Hey guys, I was wondering if I could get a little help to understand enthalpy change of combustion calculations.
I already know how to write the equations, it's just calculating it from enthalpy change of formation I have trouble with.
2. (Original post by Dotthedot50)
Hey guys, I was wondering if I could get a little help to understand enthalpy change of combustion calculations.
I already know how to write the equations, it's just calculating it from enthalpy change of formation I have trouble with.
Check out this interactive on Hess law
3. All arrows need to be facing the same direction - I go with downwards arrows. Then write the values on the corresponding arrows and calculate. Negative value is if the arrow you've drawn is in the wrong direction and positive is if its in the same direction. (I'm talking about the values in the calculation not the overall answer btw)
Thia is very hard to explain without drawing it out
4. (Original post by Manexopi)
All arrows need to be facing the same direction - I go with downwards arrows. Then write the values on the corresponding arrows and calculate. Negative value is if the arrow you've drawn is in the wrong direction and positive is if its in the same direction. (I'm talking about the values in the calculation not the overall answer btw)
Thia is very hard to explain without drawing it out
I know what you mean, thanks a bunch!

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Updated: February 22, 2016
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