C9 - Crude Oils & Fuels Flashcards
What is an alkane?
A saturated hydrocarbon with the general formula CₙH₂ₙ₊₂, for example, methane, ethane, propane
What is an alkene?
Unsaturated hydrocarbon, which contains a carbon-carbon double bond. Its general formula is CₙH₂ₙ, for example, ethene C₂H₄
What is cracking?
the reaction used in the oil industry to break down long-chain hydrocarbons into shorter-chain, more useful hydrocarbons
What is distillation?
Separation of a liquid from a mixture by evaporation followed by condensation
What is a double bond?
A covalent bond made by the sharing of 2 pairs of electrons
What does flammable mean?
easily ignited and capable of burning rapidly
What is a fraction?
Hydrocarbons with similar number of carbon atoms and boiling points separated from crude oil
What is fractional distillation?
A way to separate liquids from a mixture of liquids by boiling off the substances at different temperatures, then condensing and collecting the liquids
What is a general formula?
A formula that represents the common structure of all compounds in a single class of chemicals, For example, the general formula of alkanes is CₙH₂ₙ₊₂
What is a hydrocarbon?
A compound containing only hydrogen and carbon
What is a mixture?
a substance that contains 2 or more elements that are not chemically bonded together
What does oxidised mean?
A substance that has had oxygen added to it and/or has lost electrons
What is a saturated hydrocarbon?
A hydrocarbon with only single bonds between its carbon atoms. This means that it contains as many hydrogen atoms as possible in each molecule
What is an unsaturated hydrocarbon?
A hydrocarbon whose molecules contain at least 1 carbon-carbon double bond
What does viscosity mean?
The resistance of a liquid to flowing or pouring; a liquids “thickness”
What does volatility mean?
how readily a substance vaporizes
What is the general formula of an alkane?
CₙH₂ₙ₊₂
What are the first 5 alkanes?
Methane, Ethane, Propane, Butane, Pentane
What is the molecular formula of Methane?
CH₄
What is the molecular formula of Ethane?
C₂H₆
What is the molecular formula for Propane?
C₃H₈
What is the molecular formula for Butane?
C₄H₁₀
What is the molecular formula for Pentane?
C₅H₁₂
What is a homologous series?
a group of organic compounds with similar chemical properties who share the same general formula.
What is complete combustion?
When a hydrocarbon burns in the maximum amount of oxygen to form water and carbon dioxide
What type of reaction is complete combustion?
An oxidation reaction as the hydrocarbons gain oxygen and lose electrons. It is also an exothermic reaction as energy is released to the surroundings during the reaction
What is the equation for methane undergoing complete combustion?
CH₄(g) + 2O₂(g) -> CO₂(g) + 2H₂O(g)
What is the equation for ethane undergoing complete combustion?
2C₂H₆(g) + 7O₂(g) -> 4CO₂(g) + 6H₂O(g)
What is the equation for propane undergoing complete combustion?
C₃H₈(g) + 5O₂(g) -> 3CO₂(g) + 4H₂O(g)
What is the equation for butane undergoing complete combustion?
2C₄H₁₀(g) + 13O₂(g) -> 8CO₂(g) + 10H₂O(g)
What is the equation for pentane undergoing complete combustion?
C₅H₁₂(g) + 8O₂ -> 5CO₂ + 6H₂O
What is crude oil?
a finite resource found in rocks that is a mixture of many different compounds known as hydrocarbons. It is the remains of an ancient biomass. Most of the hydrocarbons in crude oil are alkanes.
Explain how fractional distillation works:
The crude oil is heated as it enters the fractionating column until it becomes vaporised. The vapor is then passed into the fractionating column. The fractionating column is cooler at the top than at the base. Inside the fractionating column there are many trays with holes to allow gases through. The hydrocarbons rise up the fractionating column, cooling as they rise. Once the hydrocarbon reaches its boiling point, it condenses and forms a liquid, collecting in a fraction on the tray. They are then tapped off and collected. As the hydrocarbons have different boiling points, they condense at different temperatures, and are therefore tapped off at different levels. The smaller the molecule the higher up the column they reach before condensing as they have a lower boiling point. By doing this, fractions of hydrocarbons are separated.
Are fractions pure substances or mixtures?
A mixture, the fraction boils over a range of temperatures rather than at 1 specific temperature
What are the properties of small hydrocarbons?
- Low boiling point
- High flammability
- Clean flame
- Low viscosity
- High volatility
What are the properties of large hydrocarbons?
- High boiling points
- Low flammability
- Smoky flame
- High viscosity
- Low volatility
Which properties of hydrocarbons does fractional distillation depend on?
Different boiling points
What are the 2 types of cracking?
- Catalytic cracking
* Steam cracking
What are the products of cracking?
alkanes and alkenes
Are alkanes or alkenes more reactive?
Alkenes
What is the displayed formula of Methane?
What is the displayed formula of Ethane?
What is the displayed formula of Propane?
What is the displayed formula of Butane?
What is the displayed formula of Pentane?
Are longer or shorter hydrocarbons more useful as fuels and why?
Shorter chain hydrocarbons are more useful as fuels. Longer chain hydrocarbons are more viscous, not very flammable, and burn with a dirty flame - producing a lot of smoke. Whereas, shorter chain hydrocarbons are less viscous, more flammable, and burn with a clean flame - producing little smoke
How do you test for water?
- Blue cobalt chloride paper turns pink in contact with water
- White anhydrous copper sulfate turns blue in contact with water
How do you test for carbon dioxide?
Limewater turns cloudy when carbon dioxide is present
What is incomplete combustion?
In a limited supply of oxygen, the fuel may not burn completely, forming carbon monoxide, carbon, and water
Why are alkenes more reactive than alkanes?
They contain a double bond
Why is incomplete combustion worse than complete combustion?
Incomplete combustion releases less energy than complete combustion and forms the colourless, odourless, and toxic gas carbon monoxide (it is toxic as your red blood cells pick up the gas and carry it in your blood instead of oxygen)
What reactions occur during cracking
Thermal decomposition reactions
What is the test for alkenes?
A positive test for an unsaturated hydrocarbon is that it turns orange bromine water colourless (alkanes do not react with bromine water)
What are the uses of crude oil?
- Fuels
- Polymers
- Solvents
- lubricants
- Detergents
Explain how catalytic cracking works:
1) The long-chain hydrocarbons are heated until they vaporise
2) The vapour is passed over a hot catalyst
3) The long chain hydrocarbons split apart on the surface of the catalyst to form a shorter alkane and alkenes
Explain how steam cracking works:
1) The long-chain hydrocarbons are heated until they vaporise
2) They are then mixed with steam and heated to an extremely high temperature
3) The long-chain hydrocarbon splits to form a shorter alkane and alkenes
What is a saturated hydrocarbon known as?
An alkane
What is an unsaturated hydrocarbon known as?
An alkene
Why are large hydrocarbon molecules often cracked to produce smaller hydrocarbon molecules?
- There is a greater demand for short chain hydrocarbon
- This is because shorter chain hydrocarbons are more useful as they are more flammable, less viscous, more volatile, burn with a cleaner flame, and have a lower boiling point
