Hydrocarbons Flashcards
What are the advantages of fossil fuels?
- They are available in many forms so can be used for a variety of uses. For example, coal and gas are used in power stations. Crude oil is refined into many different fractions and these are used
for varying purposes.
2.fossil fuels are always available.
What are the disadvantages of fossil fuels?
- Fossil fuels are non-renewable resources because they take millions of years to form and are being used up very quickly.
- Carbon dioxide, a greenhouse gas is formed during the combustion of hydrocarbons. These
gases are responsible for raising the Earth’s temperature and the consequential effects of this – rising sea levels and changes to crop suitability. - Acid rain is rain with a lower than expected pH. It is formed from the oxides of sulfur and nitrogen that are by-products of burning fossil fuels that contain sulfur and nitrogen. Acid rain causes damage to aquatic life, plant life and buildings and also initiates health issues for people
with breathing difficulties. - Carbon monoxide is formed when incomplete combustion of fossil fuels happens. It is extremely poisonous. Incomplete combustion occurs when there is insufficient oxygen available.
What are the reactions of alkanes?
1.Combustion
2.Halogenation
What are the products when an hydrocarbon undergoes combustion?
Water (H2O) and carbon dioxide (CO2)
What are the products when an hydrocarbon undergoes incomplete combustion?
Water(H2O) and carbon monoxide(CO).
What is done to ensure complete combustion occurs?
They are burnt in excess oxygen.
How are alkanes afffected by their size in terms of their states?
The smallest are gases (methane), larger ones are liquids (petrol) and the largest ones (candle wax) are solids.
What is the process of halogenation of alkanes?
1.Initiation- photochlorination by homolytic bond fission
2.Propagation- when a radical reacts and produces another radical.
3.Termination-when 2 radicals react
Compare the reactivity of alkanes to alkenes
Reactivity of alkenes>reactivity of alkanes as the presence of a c=c attract electrophiles.
What is another name for halogenation?
Free radical substitution
What are the uses of alkanes?
•Fuels as they burn well in oxygen
What is the function of the hydrogenation of alkenes?
It converts liquid unsaturated oils into solid, more edible saturated fats.
These are used as butter substitutes and spreads.
What are the conditions required for the hydrogenation of alkenes?
•Nickel Catalyst
•450k
•1000kPa
How do you test for alkenes?
- Add bromine to an solution
- If bromine de colourises from orange to colourless than an alkene is present.
This can be done with possasium manganate(VII) which changes from purple to colourless.
Describe the structure of a double bond
The normal bond is referred to as the sigma bond(σ) and the second bond is called the pi bond (π) this happened due to an overlap between the unhybridized p orbitals of both atoms. This presents as 2 lobes on either side of the sigma bond.
Based on carboncations how do you determine the major product in a halogenation reaction os alkenes?
The product where the halide joins to the second carboncation is produced more as the carboncation 2 is more stable and less susceptible to attack.
What is a polymer?
The joining of monomer molecules to make a large polymer molecule.
What are the uses of polyethene?
Polyethene is used to make plastic bags, buckets etc as it is flexible and unreactive.
What are the uses of polychloroethene?
Former name is PVC, used as a flexible
covering for pipes, electrical cable, etc .
What are the uses of polyphenylethene?
Former name is polystyrene and as it is hard, it is used in many household items needing strength and rigidity. Expanded polystyrene is a good insulator
What are the uses of polypropene?
It’s rigid and used in food containers and
kitchen equipment.
Why do branched polymers have lower densities and melting points?
Straight chain polymers have higher melting points and a higher density as polymers with branches as they are unable to pack closely together thus reducing the number of van der waals forces.
