Alkanes Flashcards
What are the steps in fractional distillation?
Oil is vaporised
Then passed into the column
The fractions condense at different heights
This is because there is a temperature gradient going from hot at the bottom to cold at the top
The separation depends on the boiling point of the fraction
Smaller molecules (shorter carbon chain) condense at lower temperatures
Larger molecules (longer carbon chain) condense at higher temperatures
What is cracking?
Cracking is the conversion of Large hydrocarbons to smaller hydrocarbons.
Why is cracking useful?
Cracking breaks down molecules in lower demand into molecules in higher demand and also produces alkenes which can be used for plastics.
Conditions needed for thermal cracking?
400-900 degrees Celsius
high pressure of 7000 kPa
Conditions needed for catalytic cracking?
Low pressure of 1 atmosphere
higher temperature of 450 degrees Celsius
A zeolite catalyst containing aluminium oxide and silicon oxide
What are the main products of thermal cracking?
Produces mostly alkenes
sometimes produces hydrogen used in the Haber process
What are the main products of Catalytic cracking?
Produces branch chain and cyclic alkanes and aromatic hydrocarbons
What is combustion?
Combustion is where a fuel is burnt which releases energy.
What are the products of complete combustion?
Carbon dioxide and water
What are the products of incomplete combustion?
Carbon monoxide and water and maybe soot (C)
Why do sulfur impurities in fuel contribute to acid rain?
The sulfur reacts with the oxygen when they are burnt and produce sulfur dioxide which can then react with water to form sulfurous acid which is acid rain. This acid rain kills wildlife and corrodes limestone.
Why do nitrogen impurities in fuel cause acid rain?
They react with oxygen forming Nitrogen oxide or Nitrogen dioxide to form either acidic gas or acid rain.
What are catalytic converters?
Catalytic converters remove unburned hydrocarbons and CO and NO from the exhaust gases turning them into CO₂, N₂ and H₂O.
What is special about catalytic converters? (shape, material)
They are in a honeycomb shape and they are made of catalyst metals such as Platinum, Rhodium and Palladium.
In catalytic converters why are the metals only a very thin layer?
To reduce the amount of metals needed and because it increases the surface area : Volume ratio
