2.5 Hydrocarbons Flashcards
What are some advantages of fossil fuels
Avaliable in a variety of forms so that the type of fuel can be matched with its use.
Coal and natural gas are widely used in power stations
Avaliable at all times
Abundant and have low costs
Highly exothermi
What are the disadvantages of fossil fuels
- combustion products can produce pollution
- extraction can damage the environment
- coal-fired stations need large amounts of fuel
How does acid rain form
Many fossil fuels contain sulphur so when they are combusted it produces sulphur dioxide. This reacts with water to make sulphurous acid
H20 + SO2 —— H2SO3 then oxidised to make sulphuric acid H2S03+ 1/2O2 —- H2SO4
What are fossil fuels
Substances that burn to release large amounts of heat energy (highly exothermic)
Formed from remains of dead and/or plants that were alive millions of years ago and have been changed by heat and pressure when they became trapped by rocks
Acid rain effects
Serious damages to buildings especially those that contain calcium carbonate.
Kills insect and damages aquatic life and damaging to humans with breathing problems
How do you form carbon monoxide
incomplete combustion of hydrocarbons
Carbon monoxide is toxic since it combines with haemoglobin in the blood so that this is then not avaliable to carry oxygen around the body.
Describe the reaction of alkanes in combustions
forms carbon dioxide and water if sufficient oxygen present
forms carbon monoxide if insufficient oxygen present.
Describe the reaction of alkanes with halogens
- alkanes undergo a substitution reaction with halogens in the presence of ultraviolet radiation
Takes place in 3 steps
Initiation, propagation and termination
Describe the initiation process in free radical substitution
INITIATION: starts the process
UV light has sufficient energy to break bonds homolytically producing two radicals eg Cl2 is broken down into 2 cl radicals.
Describe propagation in free radical substition
PROPAGATION: uses the radical as a reactant and forms a radical as a product this is called a chain reaction.
Cl˚+ CH4 —- CH3˚ and HCL
CH3˚ + Cl2 —- CH3Cl + Cl˚
Describe termination in free radical substition
destroying radicals=2 free radicals combine= stable molecule
-Cl• + •CH3 = CH3Cl
-CH3+ • CH3 = C2H6
-Often,termination occurs before all hydrogens are substituted by halogens.
What is the structure of Alkenes
unsaturated hydrocarbons
CnH2n
Contain a double bond in an area of high electron density making it susceptible to attack from electrophiles.
Double bond contains sigma and pi bonds that wrap around the centre of the C=C bond.
Sigma bond (σ bond)
Bond formed directly between two atoms by the head on overlap of orbitals
pi-bond (π-bond)
covalent bond formed by side-by-side overlap of p orbitals; the electron density is found on opposite sides of the carbon place
What’s the test for Alkenes
Product formed is a dibromo-alkane
bromine water orange to colourless
Whats the test for Alkenes with potassium manganate
If solution is acidic then purple solution will decolourise in the presence of an alkenes.
If the purple solution is in alkali conditions then it will turn dark green and form a dark brown precipitate
What are the C-H and C-C bond angles
C-H have bond angles of 120* (Trigonal planar)
C-C have bond angles of 109.5 (tetrahedral)
What is a photochemical reaxtion
a chemical reaction in which light (UV light) provides the energy needed to initiate the reaction
Difference in reactivity between alkanes and Alkenes
Alkanes have c-c and c-h single bonds which are sigma bonds, alkanes are unreative aside from combustion and free radical substitution
ALKENES contain at least 1 c=c double bond and c-h and c-h bonds.
It’s a region of high electron density and causes the reactive nature of Alkenes and attract electrophiles.
What is the catalytic hydrogenation of ethane
Adding h2 across a C=C in the presence of a catalyst
Nickel is the chosen catalyst as its adundant and relatively cheap
Palladium and platinum would do better but r expensive)
What is polymerisation
Large numbers of monomer molecules are combined to form a larger polymer
Occurs when Alkenes or substituted Alkenes monomers combine to form a 1 large polymer
The Alkenes are highly reactive due to their high electron density of their double bond whereas addition polymer is unreactive since it only contains sigma bonds
What are some uses of poly ethane (LPDE)
LDPE used for shopping bags as they have branched chains which create a weaker open structure since the branches keep the main polymer chains further apart. This reduces the number of van der waals forces holding the polymers together thus lowering melting temperature.
What are the uses of poly ethane (HDPE)
Laundry snd shampoo bottles, motor oils containers and recycling bins as they have straight chains. HDPE formed when polymerisation uses a Ziegler catalyst. Straight chains are produced and these pack more tightly together and hence at a higher density. The close proximity of polymer chains ALLOWS more van der waal forces per molecule hence higher melting temp
What are the uses of polypropene
Food containers
General kitchen equipment
What are the uses of polychloroethene (PVC)
Waterproof pipes
Waterproof clothing
Electrical cable insulation sheet
What are the Uses of poly(phenylethene) / poly(styrene)
Hard household packaging
Expanded polystyrene packaging
E- isomer (trans)
the isomer with the high-priority groups on opposite sides of the double bond
Z isomer (CIS)
the isomer with the high-priority groups on the same side of the double bond
