[zorokun]

Guys, can someone show me the change in enthalpy for bio diesel with the working out if possible. I need help asap!!!! I think the formula for combustion of bio - diesel (C19) is : C19H36O2 + 27O2 --> 19CO2 + 18 H2O . post any links that can help me with this too. Thank you so much if you can do this!!!!!!!!!!!!

[sjb]

One way to do this.

What bonds are being broken, what are being formed?

[Enthalpy]

Hi Zorokun, welcome!

You mean, the combustion enthalpy? Generally speaking, you have to decide whether water is produced liquid (recent central heating) or gaseous (applies better to Diesel, but be consistent in this choice when comparing fuels).

Other remark: biodiesel tend to produce a bit less heat than petrol distillates at identical mass but they're denser, which compensates when comparing per litre.

Then, the faster and safer way is to find the heat of combustion already computed, or better, measured. Certainly available on the Internet. For not too light petrol distillates it's 44MJ/kg.

Or you can compute it from the heat of formation of the fuel, of CO₂ and of H₂O (liquid or vapourr?). You need a table of enthalpies of formation, available on the Internet; this will give CO₂ and of H₂O, and either your biodiesel or similar molecules, from which you deduce your biodiesel which uses to resemble methyl palmitate. If you have an other methyl thingyate tabulated, with the same number of unsaturated bonds (probably none), adjust the length of the fatty acid by the added heat of formation of the proper number of -CH₂- groups.

Don't expect more than hints to do the job by yourself: that's how this forum works. About Asap, if you've never computed a heat of combustion, you first success will take a couple of hours, with finding the doc, understanding the signs, and all real life annoyances.

[zorokun]

Ok guys so i did some research and decided to do oleic acid from canola oil. C18H34O2 + 51/2 O2 --> 18 CO2 + 17 H2O. is this a good place to start ?

[Enthalpy]

I wouldn't start from the acid if, as is probable, your biodiesel is a methyl ester, since the heat of esterification can vary a bit. I feel better to start from a documented ester, if possible the right one, and if not, adjust the molecule length because this can be computed accurately.

What I didn't expect: why compute a heat of combustion? For a fuel it must be measured and easily accessible. That would be quicker and more reliable, because a fuel is never one pure compound.