Investigating Fuel

[chemistryishard]

i am really stuck on an investigation i am doing and my friend swont help i need help badly.

I am going to investigate and look into the study of fuels and how much energy you can burn from them, and there for I will find the fuel that contains the most energy. I will look at five fuels which are listed below:

• Methanol
• Ethanol
• Propanol
• Butanol
• Pentanol


I have to firstly work out how much energy each fuel emits, and this is where i get stuck.

Type of bond KJ mol-1
H - O 464
O = O 498.3
C - C 347
C - H 435
C = O 805
C - O 336

i have to write an equation and then balance it ad then work out how much energy each fuel emmits.

methanol



H
|
H – C – O – H CH4O
|
H

Methanol + oxygen Carbon Dioxide + Water

2CH3OH + 3O2 2CO2 + 4H2O


5704.9 KJ mol-1 is thsi the answere or do i have to do a different equation is it CH4O or CH3OH?

i neeed help!!!!!!!!!!!!!!

[TIDUSGIYA]

The molecular balance for the combustion of methanol (CH3OH) is: 2(CH3OH) + 3O2 --> 2CO2 + 4H2O or two mols of methanol require 3 mols of ?

[Vending]

chemistry is hard,

The way that you are approaching this problem is not going to work for you, i think. If you try to sum up all the energies of the bonds in the molecule of interest then you will just get a (very rough) estimate of the energy of the ENTIRE moleucle. However, when you burn things you are just breaking and forming a few bonds, not all of the bonds in the molecule.

TIDUSGIYA has the right idea. You need to either find the tabulated formulae for combustion of moleulces wich includes their heat of cumbustion OR you need to work out the heat of combustion using the stadard heats of formation for all molecules in the equation and Hess's law.

If you do not know what I am talking about let me know and I can work through an example for your using one of your fuels. THough I will be out of town for a few days, so you may have to wait.

Sorry i can't do this right now, i gotta run.

[engware]

Hi there:

Check out the following URL: http://members.aol.com/engware to get some help when dealing with fuel HHV -- enthalpy values, stoichimetry, combustion products gas composition (weight and mole basis), flame tempearture etc.

It may not help you completelly, but it will give you a good idea of what you are up to when dealing with different types of fuel.

When using some other source of information such as engineering textbooks and web sites, you might be able to put your puzzle together.

After doing some legwork, come back to the Forum and people will point you in the right direction and confirm your answers.

This is not an easy subject matter ...

Thanks,

Gordan

PS

Good Luck!

[engware]

Hi there:

I have been able to gather the heat of formation values as proposed by other Forum members and can demonstrate in a simple way how to come up with an answer for given fuel.

Here are the physical properties values -- (Perry' Cheical Engineers' Handbook):

Species MW Heat of Formation at 298 K
[kg/kmol] [kJ/kmol]

Methanol - CH4O 32 -48,080
Ethanol - C2H6O 46 -52,230
Propanol - C3H8O 60 -61,170
Butanol - C4H10O 74 -67,810
Pentanol - C5H12O 88 -260,400

Oxygen - O2 32 0
Nitrogen - N2 28 0
Carbon - C 12 0
Hydrogen - H2 2 0
Water Vapor (Liquid) - H2O 18 -285,566.4
Carbon Dioxide - CO2 44 -393,361.76


HHV of combustion is:

HHV = h products - h reactants


Since I am a mechanical engineer, I will do it for just two basic examples:

1) HHV of combustion for hydrogen

1 kmol H2 + 1/2 kmol O2 = 1 kmol H2O

2 kg H2 + 16 kg O2 = 18 kg H2O

1 kg H2 + 8 kg O2 = 1/2 kmol H2O

1 kg H2 = 1/2 * (-285,566.4)

1 kg H2 = - 142,783.2 kJ

2) HHV of combustion for carbon

1 kmol C + 1 kmol O2 = 1 kmol CO2

12 kg C + 32 kg O2 = 44 kg CO2

1 kg C + 2.66 kg O2 = 1/12 kmol CO2

1 kg C = 1/12 * (-393,361.76)

1 kg C = -32,780.14 kJ


Note: Nitrogen was never considered as part of air because it cancels itself out when balancing the combustion requirements for air.

I do hope that now you have enough information to successfully carry out your calculations.

Thanks,

Gordan

[MortenS]

Chemistryishard,
where did you get those bond energies btw? I noticed a few disrepancies to those I were able to find, especially in the C-H bond (not that strange perhaps, since C-H bonds are quite variable in bond energies)

Let me run an example for you with methanol, using the following bond energy values:

E(C-H): +413 kJ/mol
E(C-C): +347 kJ/mol
E(C-O): +358 kJ/mol
E(O-H): +464 kJ/mol
E(C=O): +805 kJ/mol
E(O=O): +498 kJ/mol

Balanced reaction:

CH3OH + 1.5O2 -> CO2 + 4H2O

To estimate the net amount of energy you get from combustion of a fuel, you can calculate the change in enthalpy between the reactants and the products.

Since breaking a bond takes energy, forming a bond releases energy.

Change in enthalpy = Sum[BE(reactants)] - Sum[BE(products)]


Left side (bonds broken)
3(C-H): 3 mol (C-H) x 413 kJ/mol = 1239 kJ
1(C-O): 1 mol (C-O) x 358 kJ/mol = 358 kJ
1(O-H): 1 mol (O-H) x 464 kJ/mol = 464 kJ
1.5(O=O): 1 mol (O=O) 1.5 x 498 kJ/mol = 747 kJ
Sum left side: 2808 kJ

Right side (bonds formed)
2(C=O): 2 mol (C=O) x 805 kJ/mol = 1610 kJ
4(O-H): 4 x 464 kJ/mol = 1856 kJ
Sum right side: +3466 kJ

Enthalphy change: Sum of bond energies reactants - sum of bond energies products = 2816 kJ - 3466 kJ = -658 kJ

1 mol of methanol equals a net release of -658 kJ at 298 K.

Compare this with the reaction energy you get if you use experimental heat of formation values (at 298K) and Hess' Law: -676.2 kJ/mol, a difference in about 2.5%. Not that large a difference in this case.

Using the same bond energy values for ethanol, I get an estimated enthalpy change in the reaction of -1276 kJ pr mol ethanol, while the enthalpy change I get when using experimental heat of formation values is -1277 kJ pr mol
ethanol, a nearly perfect match.
The differences is not that great with the other alcohols you mentioned either.


Two enthalpy calculators you might find useful:

From bond energies:
http://www.avogadro.co.uk/h_and_s/bo...ndenthalpy.htm

From heat of formation:
http://srdata.nist.gov/cccbdb/spec1_298.asp (located at http://srdata.nist.gov/cccbdb/default.htm )

The last one is nice, as it also helps you balance equations (by detecting imbalances in your chemical reactions).

[alexander]

ammonium nitrate and magnesium or alluminum powder, now that's my kind of fuel

well on the topic of fuels though, i am surpsized that nobody discusses rocket fuels... well aside from home made rocket fuels, usually amonium nitrate or amonum perclorate based fuel, there is always the rockets made by the army those are very commonly made of some sort of more explosive material, because it is easier for the army to obtain waivers and permits, because they dont actually need to, i bet they use, extremely explosive materials...

well, on the topic of cool sounding high power explosives:
amonium nitrate and fuel oil - very widely used commercial explosive, usually mixed at the site
trinitroluene (TNT) and aluminum - tritonal, commonly used as a filler in bombs and shells
ammonium nitrate and trinitroluene - amatol
pentaerythrite tetranitrate (PETN) and trinitroluene - pentolite, common ballistic explosive
trinitrophenilmethylnitramine (tetryl) and trinitroluene - tetrytol
cyclotrimethylenetrinitramine(RDX), trinitroluene and aluminum - torpex, a variation on RDX, this would be very stable compound and could possibly be used in blasting caps and detonators, and can be a base for a Composition C explosive
trinitrophenol (Picric acid) and trinitroluene - picratol, very shock sensetive, has been used since WWII in all kinds of things
lastly ednatol, which i cant find any info about, except that its an explosive, and judging from the name it contains trinitroluene (as do all of the mixtures presented even though many of the componets are themselves explosive, you add a dab of TNT and bang, you get yourself a more powerful explosive...)

oh and i claim to be no expert of any sort in explosives, but i do claim that google can do wonders and wiki is the best, other then that, if you are sad that there arent any polymer-bonded explosives on the list, then let me correct my mistake http://en.wikipedia.org/wiki/Plastic_bonded_explosive

oh and if you are wondering if the new fuel you have been developing classifies as an explosive, you can always check with the ATF: http://www.space-rockets.com/listofexp.html

[biotech7]

Hello,

Since these threads are all in conjunction with energy sources, specifiaclly combustion reactions; I wanted to ask if any one has knows about using CO2 as an energy source.
Thank you all

[biotech7]

Hello,

Since these threads are all in conjunction with energy sources, specifiaclly combustion reactions; I wanted to ask if any one has knows about using CO2 as an energy source.
Thank you all

[HydrogenBond]

Carbon dioxide is a terminal product of combustion and contains little if any combustion fuel value. Although one may combine CO2 with H2O to make an acid; H2CO3. This acid has some potential energy value, for example, the oceans are slightly basic. One could take advantage of this chemical potential to draw some energy.

Relative to the first grouping of molecules, the larger molecules have more total energy value, while the smaller ones have more energy value pound for pound. In simple terms, the terminal carbons have the most hydrogen atoms bonded to them. This is where the most energy value is. The C-C and the C-O have less in that order. As such, the smaller molecules have more umph per weight while the larger more umph per mole of molecules.

If one was designing this for an automobile, one needs to weigh the options. The smaller allows one to carry more energy value per weight which is good for fuel value and economy. However, the larger are less volatile and would therefore be safer. If we try to optimize both concerns we may decide to use something in the middle.