G of CO2 per kWh from burning methane

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SUMMARY

The discussion centers on the calculation of CO2 emissions from burning methane, specifically the claim that it yields 360 g of CO2 per kWh of energy. The user calculated a different value of approximately 178 g/kWh based on the reaction CH4 + 2O2 = 2H2O + CO2 and standard enthalpies of formation. The discrepancy was identified as stemming from a misunderstanding of the measurement context, as the original graph referred to electricity generation rather than heat energy. This highlights the importance of clarifying units when discussing energy outputs.

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Archosaur
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http://europe.theoildrum.com/node/6638" has a chart that claims that the burning of methane yields 360 g of CO2 per kWh of energy released. I decided to check that, but I'm not getting the same answer they suggest. Here's what I did:

CH4 + 2O2 = 2H2O + CO2
-74.87 + 0= 2*-285.83 + -393.509
= -571.66 + -393.509 +74.87= -890.229 kJ/mol

(all standard enthalpies of formation came from wikipedia)

CO2 is 44.011 g/mol
890.229 kJ is 0.24728583333 kWh (significant figures be damned)

44.011/0.24728583333 ≈ 178 g/kWh, as opposed to their 360 g/kWh


I can't help but notice that my answer is suspiciously close to a factor of 2 off... but my eq. is balanced...
Can someone tell me what I've done wrong?

Thanks
 
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You say per kWhr of heat, but their graph says per kWhr of electricity.
 
*slaps forehead

I figured I'd be kicking myself.
Thanks, cesiumfrog.
 

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