What is meant by the prase cracking long-chain hydrocarbons?

Question

this is chemistry

Answer 1

Thermal cracking was discovered as early as the 1860s. At high temperatures (500C) and high pressures (25 atm), long-chain hydrocarbons break into smaller pieces. A saturated C12 hydrocarbon in kerosene, for example, might break into two C6 fragments. Because the total number of carbon and hydrogen atoms remains constant, one of the products of this reaction must contain a C=C double bond.

read more here --> http://chemed.chem.purdue.edu/genchem/topicreview/bp/1organic/coal.html

Answer 2

Cracking ? I love the stuff. Its a process developed by the petrochemical companies for turning useless heavy crappy extracted oil into smaller more refined chemicals.

Rite starts like this... North Sea Oil Rig or similar dig a hole under water. Shove a pipe into it and remove a very heavy sludge like thick pastey oil from the ground. Only its full of crap and also from lying around there for millions of years under high pressure and emense heat its full of long chain hydrocarbons (chains of hydrogen and carbon). So we need to sort it or its no use to us. First it is filtered to remove all the dead sea animals and such.

Next it is heat treated "cracked" what this does is to provide enough thermal energy for the long chains to break down into smaller chains. These are more use, smaller chains include methane, ethane, butane, propane, petrol and diesel(well its smaller than crude) etc, etc.

Now they have just been cracked but are still lying in one big vat, they then pass to a major distillery where the lighter ones such as methane and ethane are removed from the top of the distillery.
(Petrol about half way up)

There are other processes that happen but these are the major ones, also the heavy stuff from the bottom of the distillery can be "recracked" until they will "crack" no more.

Answer 3

A long chain hydro-carbon can have many carbons in the chain .
cracking is the process were this long chain is broken into two shorter chains.

If we have a chain of say 15 carbons, then cracking breaks this chain into two shorter chains of say 3 carbons and 12 carbons.
Note the same number overall of carbons. 15 = 3 +12.
In the cracking process the long chain will be a 'saturated' alkane of C15H32.
The products are an 'unsaturated' alkene of C3H6 and a shorter 'saturated' alkane of C12H26.
Again note that the overall numbers of hydrogens is the same.
32 = 6 + 26 .
However long the initial chain, the number of carbons and hydrogens does not alter when the chain is cracked. It just shares out carbons and hydrogens.

Answer 4

n crude oil the light hydrocarbons such as petrol are removed and obviously useful. This leaves a thick residue called bitumen consisting of long chain hydrocarbons. Cracking of these chains gives smaller fragments. These are used in the petrochemical industry and not as fuel as the cracking process gives rise to a lot of reactive compunds such a alkenes that can be used as feedstocks in other reactions such as producing polymers.

If I remember correctly all that is needed is heat and iron to catalyse the reaction

Answer 5

I think you mean why do long chain hydrocarbons burn with a smoky flame Well the reason is that their isn't enough oxygen present to react fully with all the carbon atoms resulting in other by-products such as carbon monoxide

Answer 6

Cracking a long chain hydrocarbon breaks less useful, large molecules into more useful, small molecules

For example you could break bitumen (Also known as tar) down to two petrol fractions, which clearly would sell for more money, it's used in industry to produce mainly plastics.

Answer 7

It is a term used by the oil industry meaning heating crude oil to separate and break apart larger molecules in the crude to smaller ones. Then by fractional distillation they can separate into various products.