7.1 Carbon compounds as fuel and feedstock Flashcards
What does finite mean?
Resources that are being used up faster than being made.
Where does crude oil come from?
Ancient biomass (mostly plankton) buried and compressed underwater (in sedimentary rocks) over a long period of time.
What is crude oil?
A fossil fuel composed of different molecules (mostly hydrocarbons)
What type are most of the molecules in crude oil?
Hydrocarbons
Which elements do hydrocarbons contain?
Hydrogen and carbon only
Which homologous series do most of hydrocarbons belong to?
Alkanes
What is the general formula for alkanes?
CnH2n+2
What are the first five members of the alkane homologous series?
- Methane
- Ethane
- Propane
- Butane
- Pentane
What type of bonds do alkanes contain?
Single covalent bonds.
Draw ethane
Two carbons with lines in-between, surrounded by hydrogens connected with a line
Give the formula of the alkane containing 10 carbon atoms.
C10H22
Give the formula of the alkane containing 26 hydrogen atoms.
C12H26
Describe the purpose of fractional distillation.
To separate liquids with different boiling points into fractions for different uses.
What is a fraction?
A mixture of chemicals with similar boiling points.
What are the two main uses of fractions of crude oil?
- Fuels
- feedstocks for the petrochemical industry
Name five fractions of crude oil.
- Petrol
- Diesel oil
- Kerosene
- Heavy fuel oil
- LPG
- Bitumen
Give four useful materials made by the petrochemical industry.
- Solvents
- Lubricants
- Detergents
- Polymers
- Fuels
Describe the process of fractional distillation (5 marks)
- Crude oil heated/vaporised at ~350ºC, most hydrocarbons evaporate, and fed into fractioning column.
- This has a temperature gradient (the top is colder, the bottom is hotter).
- Molecules in crude oil have different boiling points so condense at different fractions.
- Larger molecules condense at lower fractions (HBP), Smaller molecules condense at higher fractions (LBP).
- Liquid hydrocarbons collected by pipes as fractions condense when temperature is lower than their BP.
Describe the properties of fractions from the top of the column in terms of size, boiling point, viscosity and
flammability
Top of the fractioning column:
- smaller chains of hydrocarbons.
- lower boiling point
- low viscosity
- highly flammable
What is combustion?
Burning a fuel in oxygen
What are the products of complete combustion of an alkane?
Carbon dioxide and water
Write a balanced symbol equation for the complete combustion of propane.
C3H8 + 5O2 → 3CO2 + 4H2O
What are the products of incomplete combustion of an alkane?
Carbon monoxide/carbon (particulates) and water
What is cracking?
The thermal decomposition of alkanes.
Which fractions of crude oil are commonly cracked?
Larger fractions (e.g. bitumen)
Why are these larger fractions cracked?
There is a higher supply (abundant) compared to the demand (less useful)
What are the two products of cracking?
An alkane and one or more alkenes.
What are the two types of cracking and the conditions needed?
- Catalyst cracking: zeolite catalyst at ~550ºC
- Steam Cracking: no catalyst (steam) at >800ºC
What is meant by unsaturated?
Molecules which do not have single covalent bonds (double etc,)
Describe the chemical test for alkenes.
- Add bromine water to solution.
- If solution turns colourless, alkene is present (bonded with Br)
- If solution remains brown/orange, alkane is present (no available bond).
What are alkenes used to make?
- Polymerised to make plastics (polymers)
- Hydrated to make alcohols
