Ethanol Q. (1 Viewer)

[ND]

In the success one book, for the answer to "Assess the potential of ethanol as a fuel etc..", is says:

"The most common source of ethanol is from teh addition of water to ethene. However, ethanol obtained by this method is less efficient than other fuels".

Wtf, "by this method"? Why would the method by which it's obtained affect its heat of combustion? Ethanol is ethanol... It also reads:

"The main advantage of ethanol as a fuel produced this way is that it produces a cleaner burn."

Again, wtf?

Can anyone explain, or is the book just plain wrong?

 

[spice girl]

you can get ethanol from either ethene, or from fermentation

if you get it from ethene, you're wasting money since ethene is more costly, as well as more efficient fuel than ethanol. but since ethanol is partially oxidised, it's easier to get complete combustion using ethanol.

 

[ND]

Hmm ok thanks. Their wording is pretty dodgy, they make it seem as though ethanol produced by fermentation has a higher heat of combustion and doesn't burn as clean as ethanol produced by hydration of ethene (which is what i had a problem with, seeing as the product is still obviously the same).

 

[inasero]

haha obviously not....i wouldnt bee too fazed by the wording...and also excel summary sux...make your own that way you can summarise information which is relevant to you alone

 

[Constip8edSkunk]

lol i did this yesterday and it was like wtf... ethanol obtained from ethene and by fermentation are both more costly than the fossil fuels, so i dunno why they singled one method out.... but i think its trying to say that this method derives ethanol from the petrolchemical source and from this source its far more efficient to just use octane or whatever rather than spending the energy to produce ethanol

 

[inasero]

yep i agree there....thats why brazil is so stuffed atm cos they wasted so much $$$ on an unfeasible biofuels program to completely supplemnt petrol, as opposed to blending in mixtures called "petranol" which makes much more sense

 

[toknblackguy]

hey spice girl...i thought that ethanol was more likely to undergo complete combustion because it's ignition temperature is lower than petrol, mening there is less activation energy required to get it started...or is it because its' oxidised that it has a lower ignition temperature

and anyway...what does oxidise mean

 

[spice girl]

umm it has an oxygen atom already, so burning ethanol (complete combustion) requires less oxygen than burning other alkanes/alkenes...

the black smoke / presence of carbon monixide is because there is not enough oxygen for complete combustion...

 

[Frigid]

Originally posted by ND
"The most common source of ethanol is from the addition of water to ethene. However, ethanol obtained by this method is less efficient than other fuels... The main advantage of ethanol as a fuel produced this way is that it produces a cleaner burn."

basically, what mr. seawright is trying to say is that ethanol (industrially produced by the hydration of ethene) is a less efficient fuel than fossil fuels, but since ethanol has adds more oxygen into the combustion reaction, it will have a more complete combustion, hence "a cleaner burn".

you might be confused by the wording "by this way" and be led into thinking "is there a difference between the ethanol formed by hydration and the ethanol formed by fermentation?", but you must realise, that ethanol is produced in large quantities, not by fermentation, but by hydration. as you said, ethanol is ethanol.

hope that clears everything up.

 

[ND]

Yeh, the wording is just dodgy. Thanks.

 

[eeyore]

btw, don't trust stuff in that success one chemistry book
i've found a few answers to be wrong (some of the calculation ones too) and asked my chem tutor
she said they're definately wrong and it's a dodgy book

 

[Frigid]

Originally posted by eeyore
btw, don't trust stuff in that success one chemistry book

well, care to share?

 

[toknblackguy]

the errors u get are usually one off calculation errors
i've never known a textbook to be flatly wrong about a topic