3.2 Alkanes Flashcards
What is an alkane?
A saturated hydrocarbon containing only C-H bonds
What is the general formula of an alkane?
C2H2n+2
Are akane bonds polar?
No - Carbon and Hydrogen have similar electronegativities
What intermolecular forces do alkanes have?
Only Van der Waals
Are alkanes soluble in water?
No
Name the fractions in a fractionating column in order of high to low bp and then name their uses.
- Gases - canister fuels
- Petrol - Cars
- Kerosene - Jet fuel
- Diesel oil - Lorries/cars
- Lubricating oil - candles, engine oil
- Fuel oil - Ships, power stations
- Tar/Bitumen - roads/roofing
What happens during the fractional distillation of crude oil?
- The crude oil is heated unit it is mostly vaporised
- Passed into a fractionating column that is cooler at the top than it is at the bottom
- Vapour rise up the column and condense at different points - this is collected
- The shorter the chain the higher up it condenses
How is the fracking of natural gas carried out?
- Natural gas held within shale rock
- Drill into shale, forced pressurised water and sand into rock to fracture it, collect gas
- HCL and methanol added to break up shale and prevent corrosion
What are some advantages of fracking?
- Gas supply for many years
- Reduces imported gas and electricity
What are some disadvantages of fracking?
- Lots of traffic to local area
- Concern about amount of water used
- Chemical additaves can pollute water supplies
- Small earthquakes
Why are alkanes cracked?
To turn a long chain alkane, which is not economically valuable into more economically productive shorter one
What are the conditions for thermal cracking?
- 700-1200K
- Up to 7000kPa
What are the main products of thermal cracking?
Alkenes
What are the conditions for catalytic cracking?
- Lower temperature (720K)
- Lower Pressure (but above atmospheric)
- Zeolite catalyst
- Honeycomb structure
What are the main products of catalytic cracking?
- Cycloalkanes
- Aromatic Hydrocarbons
- Branched alkanes
What is the environmental impact of nitrogen oxides?
- Forms nitric acid - acid rain
What is the environmental impact of sulphur impurities?
- Forms sulphuric acid - acid rain
What is the environmental impact of soot?
- Asthma
- Cancer
- Global dimming
What are flue gases?
Gases given out by power stations
What are catalytic converters made from?
Ceramic honeycomb coated with platinum, palladium and rhodium metals
What are greenhouse gases?
Gases which trap infrared radiation, making the earth act like a greenhouse
What is the greenhouse effect?
Greenhouse gases trap infrared radiation in the atmosphere, atmosphere heats up –> global warming
What mechanism produces halogenoalkanes?
Free Radical Substitution
What are the 3 stages of free radical substitution?
- Initiation
- Propagation
- Termination
