C9 Flashcards
what is crude oil
a finite resource found in rocks
dark, smelly liquid
mixture of hydrocarbons
how is crude oil formed
over millions of years when plankton (remains of ancient animals and plants) were covered in mud and then layers of rock were laid on top creating conditions of high pressure and temp and no oxygen to make crude oil
what is distillation
the process that separates liquids with different boiling points
what are fractions
the substances with different boiling points that crude oil is separated into
what is a saturated hydrocarbon
all the carbon - carbon bonds are single covalent bonds so they contain as many hydrogen atoms as possible in each molecule
what is the general formula for alkane molecules
Cn H(2n+2)
what are properties of a short chain hydrocarbon
low boiling point high volatility (tendancy to turn to gas) low viscosity (runny) high flammability (burns easily)
why are short chain hydrocabons generally more useful
make good fuels as they ignite and burn easily with less smoky flames
what is the process of fractional distillation
crude oil is vaporised and fed in near the bottom of the fractioning column
the column is hot at the bottom and cool at the top (temp decreases going up column)
gases move up the column and hydrocarbons condense when they reach the temp of their boiling points
what types of hydrocarbons are piped out the top of the column
the ones with the smallest molecules and the lowest boiling points (piped out as gases)
what types of hydrocarbons are piped out the bottom of the column
long chains with high boiling points that cool to form very thick liquids or solids
what are the products of a complete combustion of a hydrocarbon
carbon dioxide and water
why do we crack hyrocarbons
some heavier fractions are not in high demand. They are thick with high boiling points so hard to vaporise and don’t burn easily- not good fuels
they can be broken down into smaller, more useful hydrocarbons
where does cracking take place
at an oil refinery in steel vessels called crackers. The heavy fraction is heated to vaporise and the vapour is either:
1) passed over a hot catalyst
2) mixed with steam and heated
what reactions take place when hydrocarbons are cracked
thermal decomposition
