Organic Chemistry Flashcards
What is a hydrocarbon?
Any compound that is formed from carbon and hydrogen atoms only
Alkanes
The simplest type of hydrocarbon
CnH2n+2
Each carbon atom forms four single covalent bonds
First four alkanes are methane, ethane, propane and butane
Methane formula
CH4 H | H-C-H | H
Ethane formula
C2H6 H H | | H-C-C-H | | H H
Propane formula
C3H8
Butane formula
C4H10
What gives hydrocarbon molecules varying properties?
They vary in size
What happens to the properties of hydrocarbons as the molecules get larger?
It gets more viscous, its boiling point gets higher, the less volatile it is, the less easily it ignites
Complete combustion of hydrocarbons equation
Hydrocarbon + oxygen —> carbon dioxide + water (+energy)
Why are hydrocarbons used as fuels?
They release a large amount of energy when they combust completely
Hydrocarbon combustion waste products
CO2 and H2O
How is crude oil formed?
Over millions of years from the fossilised remains of plankton
Where is crude oil found?
In the porous rocks in the Earth’s crust
What is crude oil made up from?
Hydrocarbons
How are the components of crude oil separated?
Fractional distillation
Why does fractional distillation work for hydrocarbons?
Different sized molecules of hydrocarbons have different boiling points
What piece of equipment does fractional distillation take place in?
Fractionating column
What are the stages of fractional distillation?
1) the crude oil is heated until it evaporates
2) the molecules move up the fractionating column which is hotter at the bottom
3) larger molecules condense at the hotter bottom of the column and are collected
4) the shorter molecules condense at the cooler top of the column and are collected
Cracking
Splitting up long chain hydrocarbons into shorter chain hydrocarbons
Which hydrocarbons are more useful: long chain or short chain?
Short chain as they are flammable so make good fuels.
Long ones for, thick gloopy liquids like tar which aren’t that useful
What is the process of catalytic cracking?
1) the hydrocarbons are heated until they vaporise
2) the vapour is passed over a hot catalyst
3) thermal decomposition then takes place
What are the products of cracking?
Both alkanes and alkenes
Why are hydrocarbons split into smaller molecules?
There is a higher demand for short hydrocarbons as they easy to ignite and have low boiling points so are used in fuels
What is the main difference between alkenes and alkanes?
Alkenes have a double carbon bond
What are hydrocarbons that have double bonds described as?
Unsaturated
Alkenes have 2 fewer hydrogens compared with alkanes containing the same number of carbon atoms
What is the general formula for an alkene?
CnH2n
Why are alkenes more reactive than alkanes?
Because of the C=C bond
Why do alkenes burn with a smokier flame than alkanes?
They go through incomplete combustion
What happens in incomplete combustion?
Carbon monoxide is produced which is poisonous. Soot is given off
What happens during the combustion of hydrocarbons?
Carbon and hydrogen are oxidised, energy is released, waste products are released into the atmosphere
What two types of cracking are there?
Catalytic cracking
Steam cracking
What is the method of steam cracking?
1) vaporise the hydrocarbons
2) mix them with steam
3) heat them to a very high temperature
Balanced chemical equations for cracking etc.
Decane
HHHHHHHHHH HHHHHHHH H H
HCCCCCCCCCCH —> HCCCCCCCCH + C=C
HHHHHHHHHH HHHHHHHH H H
decane octane Ethene(alkene)
Cracking equation
Long chain hydrocarbon —> shorter alkane molecule + alkene