Efficency of Hydrocarbons (1 Viewer)

[Lukybear]

Why do lower molecular mass hydrocarbons produce the most energy per kilogram and fewest pollutants on combustion?

 

[maplestory]

Why do lower molecular mass hydrocarbons produce the most energy per kilogram and fewest pollutants on combustion?

i am not sure
maybe because of fewer dispersion forces between them
does it make sense?

 

[Lukybear]

Mabey. But i need some authority on this one.

THanks for trying anywaz.

 

[Lukybear]

Any1?

 

[Trebla]

Not too sure about more energy, but for less pollutants compare the complete combustion equations for methane versus hexane as an example.

Methane combustion:
CH₄ + 3 O₂ --> CO₂ + 2 H₂O

Hexane combustion:
C₆H₁₄ + 9.5 O₂ --> 6 CO₂ + 7 H₂O

For every mole of methane we need 3 moles of oxygen gas for complete combustion. However for every mole of hexane we need 9.5 moles of oxygen gas for complete combustion which is a lot more. Thererfore lower molecular mass hydrocarbons tend to produce less pollutants as they require less oxygen to undergo complete combustion.

 

[Gussy Booo]

Hmm, I recall something along the lines:

"Write down the equation of the hydrocarbons, and make a comparison"

I think there is a relationship. You have to count the number of moles on the LHS in comparsion to the RHS. Give it a go.

 

[Gussy Booo]

Oh here we go. I've got this written down in my book. I don't know if its relevant...though.:

"The greater the difference in moles between the left hand side and the right hand side, determines the rate and intensity of the reaction,"

To find the difference, I think you have to write down the chemical formula for the combustion of a hydrocarbon, then find the difference.

Do Methane, Ethane and Propane and see if you can find a direct relationship.

Now pollutants is related to Incomplete Combustion right?

So the less oxygen present, the more pollutants will occur. Furthermore, hydrocarbons with a lower molecular mass expressed in formulae might actually show a relationship between the necessity of oxygen.

Trial and error should get you your answers.

 

[Lukybear]

Thxs guys. But shouldnt there be some universal explanation down at the atomic level?

 

[Gussy Booo]

Combustion at the atomic level?
The breaking and forming of bonds?

To realise this, you would have to , again, play around with the formulae.

 

[Aquawhite]

I am not sure about there being a real atomic level explanation for it, but comparing balanced equations of the hydrocarbons is definitely the way to go (Y). You can always see a correlation between the amount of oxygen needed for combustion and the pollutant CO2 at the end. As the hydrocarbons get larger and larger into octance and decane, it's quite dramatic.

 

[Trebla]

If you want a basic high school level atomic level explanation without going into uni level organic chemistry (in reference to the example I mentioned), note that there are more C-H bonds in hexane than methane. Therefore more energy is needed to break all those C-H bonds in hexane than in methane.

This means that hexane absorbs more energy in order to break all bonds and thus releases less energy.

On the other hand, methane absorbs less energy to break all bonds and thus releases more energy.

In terms of getting more complete combustion, it's simply looking at the number of moles of oxygen compared to the number of moles of carbon. The more carbon you have in the hydrocarbon, the more oxygen is needed to convert it to form carbon dioxide.

 

[Aquawhite]

If you want a basic high school level atomic level explanation without going into uni level organic chemistry (in reference to the example I mentioned), note that there are more C-H bonds in hexane than methane. Therefore more energy is needed to break all those C-H bonds in hexane than in methane.

This means that hexane absorbs more energy in order to break all bonds and thus releases less energy.

On the other hand, methane absorbs less energy to break all bonds and thus releases more energy.

In terms of getting more complete combustion, it's simply looking at the number of moles of oxygen compared to the number of moles of carbon. The more carbon you have in the hydrocarbon, the more oxygen is needed to convert it to form carbon dioxide.

Exactly what I was thinking ^_^. Thanks for saying it!

+1 when I can

 

[Gussy Booo]

If you want a basic high school level atomic level explanation without going into uni level organic chemistry (in reference to the example I mentioned), note that there are more C-H bonds in hexane than methane. Therefore more energy is needed to break all those C-H bonds in hexane than in methane.

This means that hexane absorbs more energy in order to break all bonds and thus releases less energy.

On the other hand, methane absorbs less energy to break all bonds and thus releases more energy.

In terms of getting more complete combustion, it's simply looking at the number of moles of oxygen compared to the number of moles of carbon. The more carbon you have in the hydrocarbon, the more oxygen is needed to convert it to form carbon dioxide.

Fantastic! Awesome dude.

 

[annabackwards]

Exactly what I was thinking ^_^. Thanks for saying it!

+1 when I can

+2

I've apparently given out too much rep so i'll rep you when i can XD

 

[Lukybear]

If you want a basic high school level atomic level explanation without going into uni level organic chemistry (in reference to the example I mentioned), note that there are more C-H bonds in hexane than methane. Therefore more energy is needed to break all those C-H bonds in hexane than in methane.

This means that hexane absorbs more energy in order to break all bonds and thus releases less energy.

On the other hand, methane absorbs less energy to break all bonds and thus releases more energy.

In terms of getting more complete combustion, it's simply looking at the number of moles of oxygen compared to the number of moles of carbon. The more carbon you have in the hydrocarbon, the more oxygen is needed to convert it to form carbon dioxide.

That is quite brilliant. I mean the explanation of course. Would rep you, but i repped you too much already...