7.1 Carbon compounds as fuels and feedstock Flashcards
What is crude oil? Where is crude oil found? How is crude oil formed?
- A mixture of molecules, mostly hydrocarbons.
- Found in rocks;
- Formed over millions of years from remains of ancient biomass (e.g. plankton buried in mud)
What are hydrocarbons?
Molecules made up of hydrogen and carbon only (with different boiling point).
What is the general formula of alkanes?
CnH2n+2
What are alkanes?
A type of hydrocarbon which is saturated.
Why are alkanes described as saturated?
The carbon atoms in alkanes are fully bonded to the hydrogen atoms.
What are the first four alkanes?
- Methane (CH4)
- Ethane (C2H6)
- Propane (C3H8)
- Butane (C4H10)
What are the properties of hydrocarbons needed to be known? (3)
- Viscosity
- Flammability
- Boiling point
Describe the trends in the viscosity of hydrocarbons.
As the size of hydrocarbon molecules increase, they get more viscous.
Describe the trends in flammability of hydrocarbons.
As the size of hydrocarbon molecules increase, the flammability decreases.
Describe the trends in boiling points of hydrocarbons.
As the size of hydrocarbon molecules increases, the boiling point increases.
Describe the process of combustion for hydrocarbons.
- Hydrogen and carbon in hydrocarbon exothermically react with oxygen (oxidise) to produce:
- (a) complete combustion: carbon dioxide and water.
- (b) incomplete combustion: carbon or carbon monoxide and water.
What is the word and unbalanced symbol equation for the combustion of hydrocarbons?
Alkane (CnH2n+2) + Oxygen (O2) → Carbon dioxide (CO2) + Water (H2O)
How do you balance a combustion equation (with an odd number of carbon atoms in the alkane)?
Start with carbon, then hydrogen, then oxygen.
How do you balance a combustion equation (with an even number of carbon atoms in the alkane)?
- Add a 2 to the alkane
- Start balancing carbon atoms, then hydrogen, then oxygen.
Describe the process of separating crude oil using fractional distillation. (5)
- Crude oil boils as heated at 350ºC in furnace.
- Hydrocarbons evaporate and turn into gas.
- Crude oil vapour fed into fractionating column with a temperature gradient.
- Hydrocarbons move up the column and condense when they reach their boiling point
- The liquid fractions are then removed.
What happens to very long and short chained hydrocarbons during fractional distilaltion?
- Long: very high boiling points, condense quickly, removed from bottom of column.
- Short: very low boiling points, don’t condense, removed from top of column as gases.
What is a fraction?
Group of hydrocarbons with similar number of carbon atoms.
What can the fractions of the crude oil be used for? (2)
- Fuel
- Feedstock for the petrochemical industry
What are some useful fuels we depend on for modern lifestyle? (4)
- Petrol and diesel: cars and trucks
- Kerosene: jets
- Heavy duty oil: Ships
- Liquified petroleum gas: camping stoves
What are useful materials made by the petrochemical industry, depended on for modern lifestyle? (4)
- Solvents
- Lubricants
- Detergents
- Polymers
What bond do alkanes have?
Only single covalent bonds
Why is cracking useful?
Some of the products of cracking can be usefully used a fuels as there is a high demand for fuels with small molecules.
What is cracking?
A long-chain alkane is broken down (cracked) to produce smaller, more useful molecules.
What is produced during cracking? (2)
An alkane and one or more alkenes
What are some types of cracking? (2)
- Catalytic: 550ºC and [zeolite] catalyst
- Steam: 800ºC and no catalyst (steam)
Why are alkenes useful molecules? (2)
- Used to make polymers.
- Used as starting material for other useful chemicals
What is the test for alkenes? (3)
1) Add orange bromine water with solution.
2) Shake:
- (a) if solution is an alkene: bromine water turns colourless.
- (b) if solution is an alkane: bromine water stays orange
What are the missing values:
C25H52 →C20H42 + C…H…
C25H52 →C20H42 + C5H10
What are the missing values:
C40H82 → C…H… + C7H14
C40H82 → C33H68 + C7H14
