Alkanes Flashcards
What are alkanes?
They are saturated hydrocarbons containing carbon and hydrogens and do not have a double bond (4 single bonds).
What is the general formula of alkanes?
CnH2n+2
What is petroleum?
It is a mixture contains alkane hydrocarbons and can be separated using fractional distillation.
What is cracking?
It involves breaking long carbon chains into hydrocarbons and breaking the c-c bonds.
There are two types; catalytic and thermal cracking.
What is thermal cracking?
- It involves using high temperatures at 1000 °C
- Uses high pressures (up to 70ATM).
- Produces alkenes making materials such as polymers eg polyethene..
What is catalytic cracking?
- Uses high temperatures (450 °C) and slightly high pressures as well as uses zeolite catalysts.
- Produces aromatic hydrocarbons and motor fuels.
- Good to use catalysts for economic purposes as they use very little pressure and temperature saving time and speed.
Why are alkanes good fuels?
They only need to burn little fossil fuels in order for lot of energy to release.
What is complete combustion?
When oxygens been burned fully producing the products;
- Carbon dioxide (CO2) + water
What is incomplete combustion?
When there isn’t enough oxygen that has been fully burnt so producing the products;
- Carbon monoxide (CO)
- Carbon (C)
What are the issues with carbon monoxide and carbon?
- Carbon monoxide is a poisonous gas that binds to hemoglobin site where oxygen binds in red blood cells preventing oxygen from moving around the body; catalytic converters can remove them from motor fuels.
- Carbon forms soot causing breathing problems and can build in motor engines.
What are the issues with carbon dioxide?
Burning fossil fuels can produce carbon dioxide which is a greenhouse gas causing air pollution contributing to global warming.
What are unburnt hydrocarbons and how do they form ground level ozones?
- Not all hydrocarbons are burnt some are unburnt hydrocarbons.
- Oxides from nitrogen are formed when there is high pressure and temperatures in car engines making oxygen and nitrogen in the air to react with one another forming ground ozone layer which contributes to smog and causes breathing problems making it difficult to see and breathe- can be removed by catalytic converters.
How is acid rain produced?
Sulfur can be involved in burning fossil fuels where they can from sulfur dioxide which absorbs mooches in the air forming acid rain and can contribute to damaging the environment; killing vegetation and fish but can be removed from powerhouses before being released to atmospheres.
What is a free radical?
It is an unpaired electron and form when a covalent bond splits equally giving one electron to each atom.
Describe methane reacting with chlorine (chloroalkanes)
- Stage 1- Initiation reactions
Cl2 ----> 2Cl•
- Stage 2- Propagation reactions
Cl• + CH4 ---> CH3• + HCl
CH3• + Cl2 ---> CH3Cl + Cl•
- Stage 3- Termination reactions
Cl• + CH3 ---> CH3Cl
CH3• + CH3• ---> C2H6
