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March 29, 2024, 11:12:35 am

Author Topic: HEAT OF COMBUSTION IN DIFFERENT UNITS (???)  (Read 802 times)  Share 

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HEAT OF COMBUSTION IN DIFFERENT UNITS (???)
« on: March 05, 2019, 02:51:40 pm »
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Would anyone be able to explain why some fuels have a greater heat of combustion than other fuels in kJ/mol, however a lower heat of combustion than the same fuels when measured in kJ/gram???
Anyone help would be VERY much appreciate :)

Monkeymafia

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Re: HEAT OF COMBUSTION IN DIFFERENT UNITS (???)
« Reply #1 on: March 05, 2019, 03:32:01 pm »
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Great question, but just the value of KJ/mol and KJ/g is the same it's just that they are in different forms.

For example, CH4 has a molar heat of combustion of 890 KJ/mol and a heat of combustion of 55.6 KJ/g.

The difference is that 890KJ is produced per mole of CH4 and 55.6KJ is produced per gram of CH4.

Hope that makes sense.

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Re: HEAT OF COMBUSTION IN DIFFERENT UNITS (???)
« Reply #2 on: March 05, 2019, 04:54:22 pm »
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Great question, but just the value of KJ/mol and KJ/g is the same it's just that they are in different forms.

For example, CH4 has a molar heat of combustion of 890 KJ/mol and a heat of combustion of 55.6 KJ/g.

The difference is that 890KJ is produced per mole of CH4 and 55.6KJ is produced per gram of CH4.

Hope that makes sense.


Thank you! :)
Are you able to explain why for example, 1 gram of H2 releases 141 kJ of energy, which is more than 1 gram of CH4, which releases 55.6 kJ of energy. Whereas, in kJ/mol the CH4 releases more energy (890kJ) compared to H2 (which releases 282kJ)

Does that make sense?

Monkeymafia

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Re: HEAT OF COMBUSTION IN DIFFERENT UNITS (???)
« Reply #3 on: March 05, 2019, 05:43:33 pm »
+1

Thank you! :)
Are you able to explain why for example, 1 gram of H2 releases 141 kJ of energy, which is more than 1 gram of CH4, which releases 55.6 kJ of energy. Whereas, in kJ/mol the CH4 releases more energy (890kJ) compared to H2 (which releases 282kJ)

Does that make sense?

Thank you! :)
Are you able to explain why for example, 1 gram of H2 releases 141 kJ of energy, which is more than 1 gram of CH4, which releases 55.6 kJ of energy. Whereas, in kJ/mol the CH4 releases more energy (890kJ) compared to H2 (which releases 282kJ)

Does that make sense?

Ah I see what you mean. My guess is that CH4 has a higher molar mass and so, when you convert Kj/g to Kj/mol it is a much larger number than converting kj/g to kj/mol for H2. Same thing when going backwards from kJ/mol to Kj/g, dividing a large number by a large molar mass vs dividing a large number by a small molar mass.

Think that might be it.