Q's regarding 1st two Dotpoints of PoM. (1 Viewer)

[Pyramid]

After going through the first 2 dotpoints (starting to summarise, finally) I've had trouble with a few things. Any help would be appreciated


1) If butane were cracked down to ethane + ethene, ie. C4H10 --> C2H6 + C2H4, how would these 2 products be separated? My Excel textbook has a diagram in which a pipe goes from the cracking chamber to a fractionating column, where the cracked products are then separated. But given that ethane and ethene, being of similar length, have similar boiling pts, how would we get ethene on it's own?


2) Catalytic cracking requires an absence of air. Is this because alkanes burn in air to produce CO2 and H2O?


3) I know that catalytic requires:
- an absence of air
- atmospheric pressure
Does thermal cracking also require these?


4) A question from the newest Excel book:
After ethene was reacted with a certain chemical it was oxidised. The oxidised product turned litmus red. Identify the chemical reacted with ethylene.

Provided Answer: H2O
--> Could someone explain how to get to this answer?


5) When writing cracking/combustion equations for hydrocarbons, do we have to provide states when not explicitly asked for, and when conditions eg. temp and pressure are not specified? My Excel book doesn't provide any in theory or in answers.

 

[x jiim]

2. Should be because having oxygen can cause explosions, so I guess that's partly right. And 5, it's probably safer to, just in case.. iirc, they should all be gases?

I'm not sure about the other ones though =\

 

[richman92]

2. Catalysts are required to decrease the required temperature. Eg thermal cracking with no catalysts involved requires 700-1000 C while the other one is about 500

3.yes

5. cause different conditions create different products
for example, thermal cracking (700-1000C) : C11H24 -> 4C2H4 + C3H6 + H2
catalytic cracking (500 + catalysts) : C11H24 -> C9H20 + C2H4
Read more in Conquering Chem (P.6) : Thermal cracking.. decomposes the alkanes completely into small akenes such as ethylen, propene and butene. some H2 is also produced

 

[the guy]

2) u cannot get ethene on its own, only with another substance but to seperate ethene from ethane u'd have to do compression and distillation, remember, since butane ----> ethane + ethene, when seperated, it abides the law of matter.

 

[UnrealAnchovies]

Is the first one fractional distillation?