Alkanes Flashcards
State the meaning of both the words SATURATED and HYDROCARBON as applied to the term saturated hydrocarbon.
An organic compound that contains only carbon and hydrogen single bonds.
The main source of Alkanes is…
Crude oil.
Boiling points of Alkanes increase as…
The chain length increases.
Why do Alkanes with branched chains have lower boiling points than the corresponding straight chain Alkanes?
The branched Alkanes have weaker intermolecular forces due to less surface contact.
Why are Alkanes insoluble in water?
Alkanes are almost non-polar and the intermolecular forces between the water molecules (hydrogen bonds) are much stronger than the intermolecular forces between Alkanes (VdW).
Are Alkanes reactive or unreactive?
They are relatively unreactive due to having strong carbon-carbon and carbon-hydrogen bonds.
Name a process used to separate Octane from a mixture containing several different Alkanes.
Fractional Distillation.
State what is meant by the term Cracking.
Cracking is the breakdown of large hydrocarbon molecules into smaller, more useful hydrocarbon molecules.
Thermal Cracking tends to produce..
A high proportion of Alkenes.
Conditions for Thermal Cracking =
High Temperature: 700K-1200K.
High Pressure: 7000kPa.
Catalytic Cracking takes place at a…
Low Temperature (around 720K).
Low pressure.
Using a Zeolite catalyst consisting of Silicon Dioxide and Aluminium Oxide.
What are the products of complete combustion of alkanes?
Carbon Dioxide and Water.
What are the products of incomplete combustion of alkanes?
Carbon Monoxide and Water.
Why are Alkanes polar?
Alkanes are almost non-polar because the electronegativities of Carbon and Hydrogen are so similar.
The only Intermolecular forces between Alkanes are..
VdW.
Is the Combustion of Alkanes endothermic or exothermic?
Exothermic.
Name 3 greenhouse gases.
Methane, Carbon Dioxide and Water Vapour.
What are the main products of Catalytic Cracking?
Branched alkanes, cycloalkanes and aromatic compounds. Motor fuels.
Name the catalyst used in Catalytic Cracking.
Zeolite.
Write an equation for the incomplete combustion of C8H18 to form Carbon Monoxide and Water only.
C8H18 + 8.5O2 = 8CO + 9H2O
Why is a Catalytic Converter used?
To remove Carbon Monoxide from the exhaust gases in a car.
Identify a catalyst used in the catalytic converter.
Rhodium or Platinum.
State why the water produced in the exhaust gases may contribute to global warming.
Water vapour is a greenhouse gas.
Write an equation to show how Nitrogen Monoxide in the air is converted into Nitrogen Dioxide.
2NO + O2 = 2NO2.
Deduce an equation to show how Nitrogen Dioxide reacts with Oxygen and Water to form Nitric Acid.
2NO2 + 1.5O2 + H2O = 2HNO3.
Oxides of Nitrogen are also produced during the combustion of paraffin in air.
Explain how these oxides of Nitrogen are formed.
High temperature. Nitrogen and Oxygen reacting in the air.
Explain why the melting point of Dodecane is higher than the melting point of the straight-chain Alkanes produced by cracking dodecane.
Dodecane has a longer chain length/size and so it has more Van der Waals forces of attraction and therefore more energy is required to overcome this.
Why does Thermal Cracking need a high temperature?
To break the carbon-carbon bonds (and form shorter chain Alkane and an Alkene).
What are the two properties of a Zeolite Catalyst?
- They are acidic
2. They have a honeycomb structure with an enormous surface area.
What does Sulphur Dioxide contribute to?
Acid rain - it reacts with water vapour and oxygen to form Sulfuric acid.
What is the process of removing Sulphur in chimneys called and what does it involve?
Flue gas desulfurisation - Calcium Oxide (CaO) or limestone (CaO₃) is used to absorb Sulphur dioxide, producing gypsum (CaSO₄) which is used as plaster.
How does Carbon Dioxide trap heat in the Earth’s atmosphere?
Visible radiation (sunlight) penetrates the atmosphere. Infra-red radiation is emitted by the Earth - this is trapped by the greenhouse gases in the atmosphere and cannot escape.
What do unburnt hydrocarbons contribute to?
Photochemical smog and health problems.
Carbon Monoxide is a ______ gas.
Toxic/Poisonous.
What do Carbon particulates contribute to?
Asthma and cancer.
What happens to the harmful products in the Catalytic Converter?
They react with each other to produce less harmful products:
Carbon Monoxide + Nitrogen Oxide → Nitrogen + Carbon Dioxide.
Hydrocarbon + Nitrogen Oxide → Nitrogen + Carbon Dioxide + Water.
Outline the essential features of the fractional distillation of crude oil that enable the crude to be separated into fractions.
The fractions separate due to having different boiling points.
There is a temperature gradient - the column is cooler at the top.
The vapours pass up the tower via a series of trays containing bubble caps until they arrive at a tray that is cool enough to condense the vapour.
Boiling point depends on the chain length/size.
The molecules with higher boiling points are at the bottom of the column (heavier).
What is meant by the term fuel?
A material such as coal, gas, or oil that is burned to produce heat or power.
