Ethene and Ethanol (1 Viewer)

[tennille]

Is the dehydration of ethanol exothermic or endothermic? What about the hydration of ethene to make ethanol?

 

[Paroissien]

I'm not entirely sure, but I'll take a guess and so they are both endo.
Do we need to know this?

 

[tina_goes_doo]

I don't think so, or at least i bloody well hope not!

 

[tennille]

Im not sure but I saw a CSSA trial where the multiple choice asked which reaction was exothermic and 2 of the answers involved the above reactions. I don't think we have to know, though.

 

[Paroissien]

Anyway, you worried me, so I went looking for the answer.
Hydration is exothermic, and in fact so is dehydration.
And on another note, what is the best catalyst for hydration? Phosphoric acid or dilute sulfuric acid?

 

[tennille]

I would put dilute sulfuric acid. Isn't phosphoric acid for dehydration?

 

[angelicdevil]

i think diluted sulfuric acid is used for hydration and concentrated sulfuric acid for dehydration

 

[angelicdevil]

or vice versa

 

[Paroissien]

I know for certain that concentrated sulfuric acid is used for dehydration; but hydration is another matter. Different text books say different things, but I think I'll stick with dilute sulfuric acid

 

[nit]

Conc sulfuric is used for dehydration, dilute is used for any reactions in which it purely acts as a catalyst.

As for the difference between phosphoric and sulfuric acids in terms of their catalysing properties for the hydration reaction, there's not much difference. They are both required to protonate to form H+ ions which will add to the ethene double bond, so theres a good chance that the stronger acid (highest Ka) would be the better catalyst. But as both of them are strong acids (Ka -> infinity), they are likely to have very similar catalysing properties for this reaction.

 

[LSP]

also, conc sulfuric acid in dehydration reaction is used to absorb the water. hence it will produce more ethene
Conc. H2SO4
CH5OH ------> C2H4 + H2O

and for hydration, dilute H2SO4 is used.

 

[Xayma]

Make sure you put arrows both way, otherwise that formula makes no sense with the statement you just made.

C₂H₅OH <^{___Conc. H₂SO₄___}> C₂H₄ + H₂O

 

[LSP]

oh yeah, thanks

 

[mushroom_head]

But the equation is still correct if we put a one way arrow right??

 

[Xayma]

If you are saying that the concentrated sulfuric acid draws the water away then you will need double arrows otherwise if it is a one way there is no point as it will only go that way till completion.

 

[Paroissien]

Would that accept arrows like this <---> in the HSC or would you have to draw the proper ones; you know the ones I mean

 

[mushroom_head]

<--> should be fine. well it's pretty obvious that's it's a double arrow

 

[Slidey]

But geez, it's not hard to draw half an arrow going one way and another half-arrow below that going the other way.

 

[Paroissien]

Yeah, I kinda realised that, and in fact that is what I always do, but I was bored and needed the post

 

[helper]

<--> should be fine. well it's pretty obvious that's it's a double arrow

Why take the risk?