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Stiltzkin · 12-01-2004, 10:18 PM

I need an answer to this quick, quick, quick. Well moreso, an explanation of how to solve it, because I have the answer.

From the following heats of combustion,
CH3OH(l) + 3/2O2(g) --> CO2(g) + 2H2O(l) enthalpy of reaction=-726.4 KJ/mol
C(graphite) + O2(g) --> CO2(g) enthalpy of reaction=-393.5 KJ/mol
H2(g) + 1/2O2(g) --> H2O(l) enthalpy of reaction=-285.8 KJ/mol

calculate the enthalpy of formation of methanol (CH3OH) from it's elements:
C(graphite) + 2H2(g) + 1/2O2(g) --> CH3OH(l)

How the heck do I find enthalpy of formation?
I KNOW this is in the wrong board, I know where this type of question belongs, but let's face it, it could take a whole day before anyone sees it.

Please leave this here long enough for someone to help me.

I went to a review session but the TA didn't know how to explain it, she just solved it. She solved it by multiplying the first reaction's enthalpy by (-1) and the third reaction's enthalpy by (2). Afterwards she added up all the enthalpies. The problem is that I don't understand why she did that and she couldn't explain it either >.<

Please help!

12-01-2004, 10:18 PM	#1 (permalink)
Stiltzkin Junkie	PLEASE HELP! I need an answer to this quick, quick, quick. Well moreso, an explanation of how to solve it, because I have the answer. From the following heats of combustion, CH<sub>3</sub>OH<sub>(l)</sub> + 3/2O<sub>2(g)</sub> --> CO<sub>2(g)</sub> + 2H<sub>2</sub>O<sub>(l)</sub> enthalpy of reaction=-726.4 KJ/mol C<sub>(graphite)</sub> + O<sub>2(g)</sub> --> CO<sub>2(g)</sub> enthalpy of reaction=-393.5 KJ/mol H<sub>2(g)</sub> + 1/2O<sub>2(g)</sub> --> H<sub>2</sub>O<sub>(l)</sub> enthalpy of reaction=-285.8 KJ/mol calculate the enthalpy of formation of methanol (CH3OH) from it's elements: C<sub>(graphite)</sub> + 2H<sub>2(g)</sub> + 1/2O<sub>2(g)</sub> --> CH<sub>3</sub>OH<sub>(l)</sub> How the heck do I find enthalpy of formation? I KNOW this is in the wrong board, I know where this type of question belongs, but let's face it, it could take a whole day before anyone sees it. Please leave this here long enough for someone to help me. I went to a review session but the TA didn't know how to explain it, she just solved it. She solved it by multiplying the first reaction's enthalpy by (-1) and the third reaction's enthalpy by (2). Afterwards she added up all the enthalpies. The problem is that I don't understand <i>why</i> she did that and she couldn't explain it either >.< Please help! __________________ The most important thing in this world is love. Last edited by Stiltzkin; 12-01-2004 at 10:57 PM..