Comparing Decane and Octane

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In summary, the author was trying to figure out a way to supplement gasoline with nitrous oxide other than gasoline and found that, contrary to what he thought, octane has higher energy per kg than decane. He also found that, to get the same amount of energy out of a given amount of octane, you would need less decane than octane.
  • #1
462chevelle
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So I was trying to figure some random stuff out, trying to figure out something other than gasoline to supplement inject into an engine in a stand alone with nitrous other than gasoline. I know there are a bunch of things I don't know about chemistry, but I have a couple questions before I can even proceed. I took Octane and balanced the equation and found its change in enthalpy during combustion, then I found the change in enthalpy of Decane the same way. I found Decane to have a higher change in enthalpy during combustion, please correct me if I am wrong. But, i think that means that Decane has more energy per mol. Then I used a reference of -1X10^11 kJ to see how they compared for a certain amount of energy. I used the molar mass of Octane and Decane to convert these to kg used for that amount of energy. Since the molar mass of Decane is higher than Octane I found that you need less octane in kg to make this amount of energy, by quite a bit I might add. So my conclusion is that it would be a waste of time to try to use Decane. As if I even know where to find it or enough about chemistry to actually get everything working correctly. Please correct any mistakes I've made in my logic here. I'm completely self taught in Chemistry. Thanks.
 
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  • #2
This is kinda unreadable wall'o'text, this post of yours.

Decane having higher energy per mole looks OK, octane having higher energy per kg by quite a bit - not so. Energy per kg should be quite similar (not identical, but I would be surprised by difference of more than just a few percent).
 
  • #3
The OP is what happens if you take too much caffeine while pondering the difference between octane and decane.
 
  • #4
Sorry, I get a little worked up and lose all organization skills, limited on a normal day. Without my numbers in front of me octane had something like 2.8X10^6 and decane had 2.3X10^6. I attributed the different to the molar masses, octanes somewhere around 114.2 and decane somewhere around 144.4. Again, going off of memory so I could be off a few figures. And yes, I drink waaaay to much caffeine and think about stuff that is beyond my knowledge at the time of starting the thought process.
 
  • #5
462chevelle said:
octane had something like 2.8X10^6 and decane had 2.3X10^6

This is close to 10:8 - which is ratio of number of atoms of carbon in both compounds.

For linear molecules combustion enthalpy can be approximated by 2*(terminal hydrogen)+n*(-CH2- group). Non-linear molecules are quite close. This is why combustion enthalpy depends on the molar mass, but not so on the mass.

You can also think in terms of number of C-C bonds and C-H bonds. In typical molecules (ie not some exotic, strained things like cyclopropane) their energy is reasonably constant. This will be equivalent to the rule listed above.
 
  • #6
So my next question, where does a person find Decane? Is there any way for me to find out what kind of O2-Decane ratio is needed for optimal combustion? and also what kind of reactions is will have with N2O. My chem book is watered down (just a gen chem 1-2 book), I need to find a better one. If you have a recommendation that would be great.
 

1. How do the physical properties of decane and octane compare?

Decane and octane have similar physical properties, as they are both hydrocarbons with the same number of carbon atoms. However, decane has a higher boiling point and is less volatile than octane, meaning it is less likely to evaporate at room temperature.

2. Which molecule is more commonly used as a fuel?

Octane is more commonly used as a fuel because it has a lower boiling point and is therefore more volatile. This allows it to combust more easily and efficiently, making it a better choice for use in engines and vehicles.

3. How do the chemical structures of decane and octane differ?

The main difference between decane and octane is the number of carbon atoms in their chemical structures. Decane has 10 carbon atoms, while octane has 8. This difference in structure can affect their physical and chemical properties.

4. Are there any health or environmental concerns related to decane and octane?

Both decane and octane are considered relatively safe for use as fuels. However, they can both contribute to air pollution when burned, which can have negative impacts on human health and the environment.

5. Can decane and octane be used interchangeably?

Decane and octane have similar properties, but they cannot be used interchangeably in all situations. Octane is more commonly used as a fuel, while decane is used in some industrial processes and as a solvent. Additionally, their different boiling points make them better suited for different purposes.

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