đŸ”´đŸ”¸2.5 -hydrocarbons Flashcards
What is a fossil fuel
A fuel that is derived from organisms that lived long ago
What is a non-renewable resource
A resource that can’t be reformed in a reasonable timescale
What is a greenhouse gas
A gas that causes an increase in the earths temperature
Name some examples of fossil fuels
Natural gas, petroleum and coal
Name some advantages of using fossil fuels
1) available in a variety of forms allowing the type of fuel to be matched to its use e.g coal in power stations
2) can be split into fractions for varied uses e.g petroleum
3) available at all time, some green sources e.g solar and wind have limited availability
Name the disadvantages of fossil fuels
1) non renewable, formation of fossil fuels takes millions of years and reserves are being used faster than those formed
2) combustion of fossil fuels produces carbon dioxide which causes global warming and climate change
3) acid rain formation
4) formation of carbon monoxide
How does carbon dioxide cause climate change
Carbon dioxide absorbs infrared radiation from the earths surface and emits it in all directions, some goes back to the earths surface causing an increase in surface temperature
Name 2 problems caused by global warming
Rising sea levels
Changes to crop suitability
Acid rain
Carbon monoxide formation
How is nitric acid in acid rain formed
N2 (g) + O2 (g) —> 2NO (g)
2NO (g) + O2 (g) —> 2NO2 (g)
2NO2 (g) + H2O (l) —> HNO3 (g) + HNO2 (aq)
Name 3 greenhouse gases present In the atmosphere
Water
Carbon dioxide
Methane
How is sulfuric acid formed which is present in acid rain
H2O (l) + SO2 (g) —> H2SO3 (aq)
H2SO3 (aq) + 1/2O2 (g) —> H2SO4 (aq)
What damage do sulfuric acid and nitric acid in acid rain cause?
Damage to buildings especially those containing calcium carbonate
Lower pH of lakes/rivers harming aquatic life e.g fish
Damage trees/forests
Describe how fossil fuels lead to an increase in carbon monoxide
When fossil fuels aren’t burnt in excess oxygen incomplete combustion occurs forming Carbon monoxide.
CO is toxic as it binds with haemoglobinin blood so that it is not available to carry oxygen around the body
Non health related problem of carbon monoxide
Incomplete combustion is less efficient than combustion e.g a car would achieve fewer miles per litre of fuel
What is the general formula for the homologous series of alkanes
CnH(2n+2)
What is the difference between each consecutive member of the homologous series of alkanes
CH2
Do all alkanes have similar chemical reactions?
Yes as they are all saturated hydrocarbons
What states do small, larger and large alkanes have at room temperature?
Small alkanes are gases at room temp (methane), larger ones are liquids (petrol) and larger ones are solids (wax candles)
Why are alkanes non polar?
Non polar since the electronegatives of carbon and hydrogen are similar
Are alkanes reactive? What exceptions
Generally unreactive as they have no double bonds
-two important reactions = combustion and Halogenation
Define complete combustion
Combustion that occurs in excess oxygen
Define incomplete combustion
Combustion that occurs in insufficient oxygen
Is combustion exothermic or endothermic?
Exothermic as it involves a release of energy into its surroundings
What are the products of complete combustion
Carbon dioxide and water
What are the products of incomplete combustion
Carbon monoxide and water
Can sometimes form carbon as seen in black smoke from an engine
What is halogenation?
A reaction with any halogen
What is initiation
The reaction that starts the process of halogenation
What is homolytic bond fission
When a bond is broken and each of the bonded atoms receives one of the bonded electrons
What is a radical
A species with an unpaired electron
What is propagation
The reaction by which a radical is used as a reactant and forms a radical as a product continuing the reaction
What is a chain reaction
A reaction which involves a series of steps and once started continues
What is termination
The reaction that ends a process
What is a reaction mechanism
The stages by which a reaction proceeds e.g reaction mechanism for halogenation is initiation, propagation, and termination
What is a substitution reactions
One where one atom/group is replaced by another atom/group
What are the conditions for halogenation to occur
Alkanes don’t react with halogens in the dark :: they must be exposed to UV light (often sunlight) to react
What are the 3 stages of halogenation
1) initiation
2) propagation
3) termination
Describe initiation in detail
1) UV light has sufficient energy to break Cl-Cl bond (any halogen) homolytically.
2) homolytic bond fission occurs when each of the bonded atoms receives one fo the bond electrons so radicals are formed
3) radicals react indiscriminately to gain another electron and form a pair
Equations for initiation
Cl2 —> 2Cl •
Note: • = radical
Describe propagation in detail
1) Radicals are very reactive and take part in a series of propagation reactions
2) chain reaction occurs.
Equations for propagation
Cl• + CH4 —> CH3• + HCL
CH3• + Cl2 —> CH3Cl + Cl•
Describe termination in detail
Propagation continues until 2 radicals meet causing reaction to stop.
Equation for termination
Cl• + CH3• —> CH3Cl
Why are alkanes unreactive and why are radicals reactive
Alkanes are unreactive because they are non polar and do not contain double bonds whereas radicals are very reactive because they have an unpaired electron
What is a π bond
A bond formed by the sideways overlap of p electrons
What is the general formula of alkenes
CnH(2n)
When are alkenes formed?
When petroleum is cracked
Why are alkenes much more reactive than alkanes?
Due to their double bond
What is a main use of alkenes
Important starting material for a variety of organic synthesis reactions e.g polymerisation
According to VSEPR theory which shape/bond angle is Ethene
Planar triangular with a bond angle of 120 degrees
What does a pi bond have
A pi bond has an area of High electron density above and below the plane of the molecule
Why are alkenes not used as fuels
They have to be manufactured from alkanes :: it is more cost effective to use alkanes directly themselves
Name the general bond angles in other alkenes
120 degrees between hydrogen bonds attached to the double bonded carbon atom
109.5 degrees between hydrogen bonds attached to normal sigma carbon atoms
What is an electrophile
An electron deficient species that can accept a lone pair of electrons
What is heterolytic bond fission
When a bond is broken and one of the bonded atoms receives both the bonded electrons
What is an addition reaction
A reaction in which reagents combine to give one product
How many electrons do alkenes have in pi orbital
What does this mean
Pair of electrons
This means they are susceptible to attack by an electrophile
(LEARN DIAGRAMS IN BOOK)
What is added to a substance to identify an alkene
What happens as a positive result
Bromine/bromine water as it tests for unsaturated hydrocarbons
Decolouration of Brown bromine water
Why is bromine water used instead of liquid bromine
Because liquid bromine is very corrosive
What process occurs if you add hydrogen to an alkene
Hydrogenation
What catalyst is used during hydrogenation
Transition metals such as platinum but nickel is most commonly used as its cheap
Name a use of hydrogenation
Liquid vegetable oils are polyunsaturated (many double bonds) can be made saturated by adding hydrogen hardening oil to make solid edible fats (butter)
What are the two possible products of the reaction between propane and hydrogen bromide
1-bromopropane
2-bromopropane
2-bromopropane is produced more frequently
Why is 2 bromopropane the more dominant product of the reaction between propene and hydrogen bromide
Because the carbocation is more stable because alkyl groups tend to release electrons to become (^+) spreading (delocalising) the positive change and stabilising the ion. This means 2 carbocations as featured in forming 2-bromopropane are more stable than 1.
What is polymerisation
The joining of a large number of monomer molecules to make a large polymer molecule
What is a monomer
A small molecule that can be made into a polymer
What undergoes addition polymerisation?
What is it?
- Alkenes and substituted alkenes
- This means that the double bond is used to join the monomers and only 1 product forms
What is formed when Ethene undergoes addition polymerisation
Polyethene commonly called polythene
Now does not contain double bond but involves ene
Name some properties of polythene
Unreactive, flexible, solid used to make plastic bags
What was influential in producing hard plastic
Catalysts such as Ziegler catalysts meant that chains could align closer, strengthening van der Waals forces and producing harder higher density plastic
Now had a higher melting point
What is a repeat unit
The section of the polymer that is repeated to make the whole structure
What is the use of polypropene
Rigid plastic used in food containers and general kitchen equipment
(LEARN DIAGRAM Pg 143)
What is a use of polychloroethene
PVC
Used In water pipes, waterproof clothing etc
LEARN DIAGRAM Pg 144
What is a use of polyphenylethene
Polystyrene
Insulator in packaging
