Cracking Flashcards
Cracking
Cracking is thermal decomposition of large chained alkanes to make shorted chained alkene and alkane
What is cracking use for?
Cracking is use to convert fraction containing large hydrogen carbons molecular which are less useful and into smaller more useful hydrocarbons. Kerosene oil and diesel oil are often cracked to make gasoline and hydrogen
Thermal cracking
Thermal cracking fraction containing large alkane are heated at a high pressure at temperatures above 700 A mixture and of smaller alkanes and alkenes is formed
Catalyst cracking
Catalyst cracking is kerosene oil or diesel oil fraction passes through a mixture of silicon oxide. The aluminum oxide 400-500, the oxide mixture act as a catalyst. Catalyst cracking produces relatively high proportion of hydrocarbons use in gasoline (petrol).
Combustion of alkane
Alkane burn with a clear blue flame
In presence of excess air we say in which the alkane is in incomplete combustion
These are oxidation reduction reactions. In which the carbon and hydrogen are oxidized and the oxygen is reduced
The flame produced from incomplete combustion can be yellow and sooty because of the unreacted carbon particles present.
Use of alkane
Alkane are good fuel because burn clearly, release a lot of energy on combustion.
Gaseous alkane such as methane, propane and butane are used for fuel in bottle gas.
LPG ( liquefied petroleum gas) is use as fuel in cars. A mixture of liquid alkane is used for a variety of fuel.
Liquid alkane is use as a solvent for a variety of of organic substances eg marking pens
Combustion of alkene
Alkene have high ration of carbon to hydrogen than alkane
When they burn in air, in addition to carbon dioxide and water carbon monoxide and the unreacted of carbon particles are also formed.
The carbon particles in flame are yellow sooty ( blackish)
We can use the colour of flame for a rough guide to distinguish between alkane and alkene when burn in the air.
