Ethanol Question (1 Viewer)

[Libbster]

I have a question from a past paper and I can't work it out:

Explain the need for a catalyst for the reaction that produces ethanol from ethene:
a The reaction is very slow because ethene is not water soluble
b The reaction is reversible and ethanol goes back to ethene
c The reaction reaches an equilibrium that favours the reactants
d The reaction is endothermic and ethanol decomposes at high temperatures

Originally i was leaning towards a but the reaction is slow because the moleules don't want to give away their O and H molecules, so now I'm thinking d.

I also have another q that doesn't make sense

Which substanes can be produced by condensation polymerisation reactions?
a Ammonia and water
b Cellulose and polyvinyl chloride
c Protein and polyethylene
d Polysaccharides and polystyrene

I don't think any of them are right, as PVC, polystyrene and polyethylene are addition. Water can be produced from condensation but I'm not to sure about ammonia

Help would be appreciated

Thanks!

 

[richz]

1) A
2) i agree with u im not sure but as u said PVC, polyethene, and styrene are addition. So my guess is A

 

[LaCe]

1) a) is correct, as it is not an equilibrium reaction, although the equation does work both ways (i.e. hydration and dehyration)
2) a) is correct because water and NH3 are produced from condensation polymerisation, and the fact that the other polymers are formed by addition reactions (NH3 can be released from condensation polymerisation but water is the most common one)

 

[Libbster]

Thanksfor the help! When you think about it, condensation polymerisation forms a polymer and a 'small molecule' is condensed out.

 

[LaCe]

yeah the small molecule is usually water but in some cases (very few) it is ammonia

 

[xiao1985]

yeah the small molecule is usually water but in some cases (very few) it is ammonia

can be of water, ammonia, HCl...
doesn't really have to be water... depend on the reactants u use... doesn't even have to be "mostly"...

 

[Abtari]

hydration question

I have a question from a past paper and I can't work it out:

Explain the need for a catalyst for the reaction that produces ethanol from ethene:
a The reaction is very slow because ethene is not water soluble
b The reaction is reversible and ethanol goes back to ethene
c The reaction reaches an equilibrium that favours the reactants
d The reaction is endothermic and ethanol decomposes at high temperatures

Originally i was leaning towards a but the reaction is slow because the moleules don't want to give away their O and H molecules, so now I'm thinking d.


Thanks!

well, i know that you need a catalyst because water doesn't just spontaneously react with ethene. There is no 'incentive' for water to react chemically with ethene. I though A was about a physical reaction (dissolution) and didnt have anything to do with "reacting". I know its not a reversible reaction but i dont recall reading about ethanol going back to ethene. C is definitely wrong. D seems plausible to me. What is the answer?

For me, none of them seem to give a direct answer to the question but i would have to go for D.

ideas...anyone? thanx

 

[xiao1985]

the main reason why u want to add catalyst is to accelerate the reaction...

so i would go for a... tho wut follows is abit =S

 

[Abtari]

according to A:

The reaction is very slow because ethene is not water soluble

but what does reaction speed have to do with solubility? not picking a fight or anything just wondering how a physical change can help in a chemical reaction..

help!

 

[Sirius Black]

My personal guess

Since ethene is non-polar thus it doesn't tend to dissolve in water therefore, the electron-rich(I forgot the scientific name for it,sorrie) water molecules (as there are two lone pairs on Oxygen) would not be able to attack ethene. By adding H+, ethen becomes free radicals which can be attacked by water molucles hence the faster reaction rate will result right?

 

[m_isk]

according to A:

The reaction is very slow because ethene is not water soluble

but what does reaction speed have to do with solubility? not picking a fight or anything just wondering how a physical change can help in a chemical reaction..

help!

Tha answer is A. Also, a physical change can help in a chemical reaction. When you write any equation eg C2H2 + H20 --> C2H50H, what is actually happening. Well, a molecule of ethene COLLIDES with a molecule of water. Since ethene is not water soluble, it is a solid when placed in water. This means that the molecules are all tied up and there is a much less chance of collisions between ethene and water molecules occuring. However, if we add the catalyst concentrated H2S04, the ethene dissolves, ie all the molecules are jumping around all over the place, collisions are much more likely, and the production of the products is favoured. Thus a physical change CAN help in a chemical reaction. :uhhuh:

Edit: BTW which paper was that question from??

 

[Libbster]

They were questions from last years half yearly exam. My school is Maitland Grossmann (it's near Newcastle) and our chemistry teacher told us that he wrote the paper, though i'm not quite sure because he has said that before and we were actually doing the independent schools paper.