Heat of Combustion (1 Viewer)

[WEMG]

For my independent investigation, I'm doing the heat of combustions of hydrocarbons. I was absent from school on the day my teacher explained to the class on how to perform the investigation. I have already researched the topic but I am still unsure about something. Is it true that if a hydrocarbon has more carbons it releases more heat? I need to confirm this because I am writing up my hypothesis.

Thanks in advance.

 

[DNETTZ]

Energy is produced in a chemical reaction when the energy needed to start it is less than the energy produced in the reaction. (Exothermic)

<dl><dd>CH₄ + 2 O₂ → 2 H₂O + CO₂ + Energy</dd></dl> or

<dl><dd>C₃H₈ + 5 O₂ → 4 H₂O + 3 CO₂ + Energy</dd></dl> <dl><dd>C_nH_2n+2 + (3n+1)/2 O₂ → (n+1) H₂O + n CO₂ + Energy</dd></dl>

However, note that as the amount of Carbon atoms increases, it requires increasing huge amounts of oxygen to fuel the reaction.

Therefore, incomplete combustion occurs instead and as a result, the larger the hydrocrabon, the less effeciently it will burn and less energy per gram than recorded will be released. (Not less than other hydrocarbons untill they start getting small)

For incomplete combustion:

Fuel + Oxygen -------> Carbon Monoxide +Carbon Dioxide + Carbon + Water + Hydrogen Gas + Fuel
Any of the by-products, but NOT necessarily ALL will be formed.

Continued....

 

[DNETTZ]

Ummm, that was long, so

Bigger Hydrocarbons = more energy
because they break more bonds.
heres the proof. The other post was wrong, i misinterpreted.

Heres the experiment and the theory.

 

[WEMG]

So if enthalpy decreases wouldnt that mean heat of combustion increase? And from that table it would mean that the more carbon there are the higher the heat of combustion. I'll just base my hypothesis on the theoretical values and account for the discrepancies due to incomplete combustion.

Thanks for the help!

Edit: One more thing, I don't have a clue how I will perform the experiment ie, equipment needed, method etc. The investigation asks us to "Compare the heat of combustion of methane and ethanol."

 

[DNETTZ]

So if enthalpy decreases wouldnt that mean heat of combustion increase? And from that table it would mean that the more carbon there are the higher the heat of combustion. I'll just base my hypothesis on the theoretical values and account for the discrepancies due to incomplete combustion.

Thanks for the help!

Edit: One more thing, I don't have a clue how I will perform the experiment ie, equipment needed, method etc. The investigation asks us to "Compare the heat of combustion of methane and ethanol."

COME BACK I WAS SLIGHTLY WRONG! See above word document for clearer points, and i reduced my arguement down to a few lines.
Incomplete combustion still applies, thankfully.

Use the q=m delta t equations to work out the energy released from the mass. Compare to theoretical calues, you know how that works.

Substitute parrafin in the above one for methane and then ethanol.

How did you get methane, btw? Its pretty hard to burn that stuff because highschools dont like explosive gases?

Experiment outline provided in above word document. Replace their tea candle with a spirit burner filled with methane and ethanol as I recall. Corrupt the gist of it into your experiment. Basically, use the heat of water to measure the energy produced and released from the combustion!


Cheers!

 

[DNETTZ]

<table class="MsoNormalTable" style="border-collapse: collapse; border: medium none;" border="1" cellpadding="0" cellspacing="0"> <tbody><tr style=""> <td style="width: 77.4pt; border: 1pt solid windowtext; padding: 0cm 5.4pt;" valign="top" width="103">

Hydrocarbon<o></o>​

</td> <td style="width: 126pt; border-width: 1pt 1pt 1pt medium; border-style: solid solid solid none; border-color: windowtext windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="168">

Formula<o></o>>​

</td> <td style="width: 117pt; border-width: 1pt 1pt 1pt medium; border-style: solid solid solid none; border-color: windowtext windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="156">

Heat of Combustion<o></o>>​

(kJ/g)<o></o>>​

</td> <td style="width: 122.4pt; border-width: 1pt 1pt 1pt medium; border-style: solid solid solid none; border-color: windowtext windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="163">

Molar Heat of Combustion (kJ/mol)<o></o>>​

</td> </tr> <tr style=""> <td style="width: 77.4pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="103">

Methane<o>></o>>​

</td> <td style="width: 126pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="168">

CH₄<o>></o>>​

</td> <td style="width: 117pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="156">

55.6<o>></o>>​

</td> <td style="width: 122.4pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="163">

890<o>></o>>​

</td> </tr> <tr style=""> <td style="width: 77.4pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="103">

Ethane<o>></o>>​

</td> <td style="width: 126pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="168">

C₂H₆<o>></o>>​

</td> <td style="width: 117pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="156">

52.0<o>></o>>​

</td> <td style="width: 122.4pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="163">

1560<o>></o>>​

</td> </tr> <tr style=""> <td style="width: 77.4pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="103">

Propane<o>></o>>​

</td> <td style="width: 126pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="168">

C₃H₈<o>></o>>​

</td> <td style="width: 117pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="156">

50.0<o>></o>>​

</td> <td style="width: 122.4pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="163">

2200<o>></o>>​

</td> </tr> <tr style=""> <td style="width: 77.4pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="103">

Butane<o>></o>>​

</td> <td style="width: 126pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="168">

C₄H₁₀<o>></o>>​

</td> <td style="width: 117pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="156">

49.3<o>></o>>​

</td> <td style="width: 122.4pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="163">

2859<o>></o>>​

</td> </tr> <tr style=""> <td style="width: 77.4pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="103">

Pentane<o>></o>>​

</td> <td style="width: 126pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="168">

C₅H₁₂<o>></o>>​

</td> <td style="width: 117pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="156">

48.8<o>></o>>​

</td> <td style="width: 122.4pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="163">

3510<o>></o>>​

</td> </tr> <tr style=""> <td style="width: 77.4pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="103">

Hexane<o>></o>>​

</td> <td style="width: 126pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="168">

C₆H₁₄<o>></o>>​

</td> <td style="width: 117pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="156">

48.2<o>></o>>​

</td> <td style="width: 122.4pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="163">

4141<o>></o>>​

</td> </tr> <tr style=""> <td style="width: 77.4pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt;" valign="top" width="103">

Heptane<o>></o>>​

</td> <td style="width: 126pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="168">

C₇H₁₆<o>></o>>​

</td> <td style="width: 117pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="156">

48.2<o>></o>>​

</td> <td style="width: 122.4pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt;" valign="top" width="163">

4817<o>></o>>​

</td> </tr> <tr style="height: 4.9pt;"> <td style="width: 77.4pt; border-width: medium 1pt 1pt; border-style: none solid solid; border-color: -moz-use-text-color windowtext windowtext; padding: 0cm 5.4pt; height: 4.9pt;" valign="top" width="103">

Octane<o>></o>>​

</td> <td style="width: 126pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt; height: 4.9pt;" valign="top" width="168">

C₈H₁₈<o>></o>>​

</td> <td style="width: 117pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt; height: 4.9pt;" valign="top" width="156">

47.8<o>></o>>​

</td> <td style="width: 122.4pt; border-width: medium 1pt 1pt medium; border-style: none solid solid none; border-color: -moz-use-text-color windowtext windowtext -moz-use-text-color; padding: 0cm 5.4pt; height: 4.9pt;" valign="top" width="163">

5450<o>></o>>​

</td> </tr> </tbody></table>

Found these on the interwebs for ya, they make MUCH more sense like the previous graphs, which showed the wrong thing.

 

[WEMG]

COME BACK I WAS SLIGHTLY WRONG! See above word document for clearer points, and i reduced my arguement down to a few lines.
Incomplete combustion still applies, thankfully.

Use the q=m delta t equations to work out the energy released from the mass. Compare to theoretical calues, you know how that works.

Substitute parrafin in the above one for methane and then ethanol.

How did you get methane, btw? Its pretty hard to burn that stuff because highschools dont like explosive gases?

Experiment outline provided in above word document. Replace their tea candle with a spirit burner filled with methane and ethanol as I recall. Corrupt the gist of it into your experiment. Basically, use the heat of water to measure the energy produced and released from the combustion!


Cheers!

Sorry I meant methanol! Yes I read the document. But I dont understand why the molar heat of combustion increases but the normal heat of combustion decreases.

EDIT: Don't worry, forgot to read the molar heat of combustion part!

Thanks! The doc cleared up a lot of things for me!

 

[DNETTZ]

Welcome!