7. Organic Chemistry
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What is a hydrocarbon?
any compound thats formed from carbon and hydrogen only
What is crude oil?
Crude oil is a finite resource found in rocks. the remains of an ancient biomass consisting mainly of plankton that was buried in mud a mixture of a very large number of compounds
What are many of the compounds in crude oil?
Hydrocarbons - mostly alkanes
What is an alkane?
Contains a single chains of carbon atoms with hydrogen atoms bonded along the side every C atom has 4 single covalent bonds
What is the general formula for the homologous series alkanes?
CnH2n+2
What is the simplest alkane?
Methane CH4
What are the four simplest alkanes?
Methane- CH4, ethane- C2H6, propane- C3H8 and butane- C4H10
What is a molecular formula?
Gives number of atoms of each element in a molecule
What is a structural formula?
Shows the atoms molecule by molecule
What is the displayed formula?
Shows how atoms are arranged and the bonds between them
What happens as the length of carbon chain increases
Boiling point increases because more energy is needed to break the intermolecular forces more viscous
combustion equation
hydrocarbon+ O2 –> C02+ H20
Gases in fractional distillation which have the lowest boiling point also are…
The most volatile and flammable
What is viscosity?
The resistance of flow that a liquid has
what is fractional distillation
heating crude oil up and separating out different compounds ( based on boiling point)
steps of fractional distillation
• heat crude oil to a very ^ temp so all compounds have evaporated to gad • the hot gaseous hydrocarbons (HC) rise up the fractionating column • as they rise they cool down as the top of the column= cooler • HC condense as become cooler than their bp - liquid HC collect in trays and drain out • longer chain HC condense at bottom as = high bp shorter chain HC condense at top as = lower bp
What happens in fractional distillation as molecule size decreases in terms of colour?
Becomes lighter: black, yellow, transparent
Why are hydrocarbons cracked?
Long chains are not useful as they are thick, viscous liquids =poor fuels
what is cracking
thermal decomposition reaction
What types of cracking are there?
Thermal and catalytic cracking
Why are fractions with large hydrocarbon molecules more viscous?
Longer chains are easily entangled. The amount of intermolecular force also affects viscosity
How is thermal cracking carried out?
Long hydrocarbon chains are vaporised, mixed with steam and placed under high pressure and temperatures (~750c) and thermal decomposition takes place - chains are split apart
How is catalytic cracking carried out?
Long hydrocarbon chains are vaporised and passed over a hot catalyst (powdered AlO)- heat to a high temperature (~500c). Chains cracked as thermal decomposition takes place
What is a disadvantage of thermal cracking?
There is not a lot of control over what products are formed