Hydrocarbons
alkane is a simple type of hydrocarbon
each carbon atom can four 4 bonds
each hydrogen atom can only form 1 bond
methane (CH₄)
alkanes are a homologous series
have similar chemical properties
ethane (C₂H₆)
propane (C₄H₁₀)
butane C₆H₁₄
saturated hydrocarbon, making them relatively unreactive
general formula = CₙH₂ₙ₊₂
obtained from the fractional distillation of crude oil
the suffix of the name indicates the type of compound (-ane for alkane)
prefix of the name indicates the number of carbon atoms
hydrocarbons come from crude oil
crude oil is formed from dead prehistoric organisms (e.g. algae) getting buried at the bottom of the sea. the heat and pressure turns them into oil over millions of years
consists of a range of different hydrocarbons with different boiling points
the more carbons in the alkane, the higher the boiling point
fractional distillation is used to separate fractions
properties
the longer the chain (the more carbon atoms), the higher the boiling point
the shorter the chain, the more volatile it is
the lower the boiling point, the higher the volatility
the longer the chain, the higher the viscosity (thick)
the lower the boiling point point (shorter the chain), the more flammable it is
suffix of hydrocarbon = the type of hydrocarbon; prefix = number of carbon atoms in the longest chain
longer chain hydrocarbons are less in demand
short chain hydrocarbons are in huge demand because they can be burnt in for fuel
cracking converts these into short chain hydrocarbons + an alkene
process of thermal decomposition
catalytic cracking = alkanes are heated to vaporise them + pass them over a hot catalyst (aluminium oxide), which splits the alkane
steam cracking = alkane is heated to vaporise them (gas) + is mixed with steam and heated to a high temperature, which splits the alkane
alkene is used to make plastics
causes one of the carbon bonds to break
the shoter alkane will take the hydrogen from the alkene to fill it, and the alkene will bond two carbon atoms to each other to overcome the shortage of hydrogen atoms
they make the best fuels
long chain alkane → shorter alkane + alkene
no. of carbon and hydrogen atoms should be the same
e.g. decane (10) → heptane (7) + propene (3)
alkenes have double bonds, so are unsaturated hydrocarbons
form CO2 and H2O when they undergo complete combustion
alkane + oxygen → carbon dioxide + water
long chains could be solids, while short chains are gases
alkanes release lots of energy when burnt with oxygen, which makes them goof duels
alkane + oxygen → carbon monoxide/carbon (soot) + water (incomplete combustion)
carbon monoxide is very toxic
you can't know which product you're going to get with water
depends on the amount of oxygen present