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developing fuels 2 (df5-df11) (fuels (how to handle problems (governments…
developing fuels 2 (df5-df11)
catalysts
catalysts increase the rate of reactions
a catalyst= increases the rate of reaction by providing an alternative reaction pathway with lower activation energy. it is unchanged at the end of the reaction
catalysis= speeding up a chemical reaction by using a catalyst
most catalysts only catalyze one specific reaction
catalysts are used in cracking
short chain hydrocarbons are more useful than longer ones e.g. petrol
long chain alkanes can be cracked into smaller hydrocarbons (including alkenes)
e.g. C16H34(g)---> C7H14(g) + C9H20(g)
the products of cracking are RANDOM- the same molecule can give different products
without a catalyst cracking requires v high temps and pressures which is expensive
by passing a hydrocarbon vapour over a heated solid catalyst cracking can take place at lower temps (450) and pressures- saving money
heterogeneous catalysts
a heterogeneous catalyst= a catalyst in a different physical state from the reactants
a homogeneous catalyst= a catalyst in the same state as the reactants
e.g. iron in the haber process is a solid which catalyses the reaction between nitrogen and hydrogen gas
catalytic converters
platinum is a heterogeneous catalyst
convert toxic pollutants into harmless or less harmful gases
reactions on heterogenous catalysts
1) reactant molecules arrive at the surface and bond with the solid catalyst- adsorption
2) the bonds between the reactants atoms are weakened and broken up. this forms RADICALS (atoms/molecules with unpaired electrons). these radicals bond together to form new molecules
3) the new molecules are detached from the surface of the catalyst- desorption
catalysts can be poisoned
preventing them from working
heterogeneous catalysts often get poisoned because the poison bonds to the catalysts surface more strongly than the reactant
so the catalyst is prevented from getting involved in the reaction that its speeding up
organic groups
alkanes are saturated hydrocarbons
general formula= CnH2n+2
every carbon atom in an alkane forms
4 single bonds
with other atoms
it is impossible for carbon to make more than 4 bonds so alkanes are saturated
cycloalkanes
a ring of carbons with 2 hydrogens attached to each carbon
general formula= CnH2n
they are still SATURATED
alkenes are unsaturated hydrocarbons
general formula= CnH2n
alkene molecules all have at least one
C=C double covalent bond
the double bonds cause them to be unsaturated because they can bond to extra atoms in addition reactions
cycloalkene
general formula= CnH2n-2
has 2 fewer hydrogens than an open chain alkene
Benzene has a ring of delocalised electrons
Benzene (C6H6) is like a cyclic alkene with 6 carbons and 3 double bonds
its more stable/ less reactive because the double bond electrons are delocalised around the carbon ring (not attached to any particular carbon) - that's why they have a circle nside
compounds with benzene rings are called ARENES or AROMATIC COMPOUNDS
alcohols contain oxygen
general formula= CnH2n+1OH
OH is hydroxyl group
shapes of organic molecules
electron repulsion helps explain the shapes of moleculoes
electron pairs repel eachother
so molecules take the shape that allows all the pairs of electrons to get as far from eachother as possible
single bonded carbon atoms have bonds arranged in tetrahedral
when carbon atoms make 4 bonds (alkanes) the molecules forms tetrahedral
angle= 109.5 degrees
this tetrahedral shape means that single bonded carbon chains form zig zags
atoms around a double bonded carbon form a trigonal planar
the C=C double bond and the atoms bonded to these carbons are planar
angle= 120 degrees
sigma and pi bonds
single bond
single bonds in organic molecules are sigma
formed when 2 orbitals overlap in a straight line in a space between two atoms
gives the highest possible electron density between the 2 positive nuclei so sigma bonds are strong
double bond
made up of a sigma and pi bond
a pi bond is formed when two p orbitals overlap sideways. its got 2 parts one above and one below the molecular axis
a pi bond is weaker than a sigma bond - this means that a double bond is less than twice as strong as a single bond
isomerism
structural isomers have different arrangements of atoms
different carbon skeleton
the carbon skeleton can be arranged differently e.g. straight chain or branched
these isomers have similar chemical properties
physical properties e.g. boiling point will be different because of the change in the shape of the molecule
functional group in different place
functional group could be attached to a different carbon atom
have different chemical and physical properties
different functional groups
the same atoms can be arranged into different functional groups
they have very different chemical and physical properties
E/Z isomerism
atoms cannot rotate around double bonds
very rigid /don't bend
restricted rotation causes E/Z isomerism
E/Z isomerism is stereoisomerism
stereoisomers have the same shorted structural formula but a different arrangement in space
due to lack of rotation around the double bond some alkenes have stereoisomers
E= hydrogen atoms on different sides of the double bond
Z= hydrogen atoms on the same side of the double bond
cis and trans
cis= z isomer
trans= e isomer
addition reactions of alkenes
reacting alkenes with water and H2SO4 catalyst makes alcohols
ethanol is manufactured by steam hydration
the reaction is reversible and the yield is low but the unreacted ethene gas can be recycled to make the yield higher
ethene can be hydrated by steam at 300 degrees Celsius and 60atm and a solid phosphoric acid catalyst
2) if you add cold water and warm the product it is hydrolysed and form an alcohol
1) cold concentrated sulfuric acid reacts with an alkene in an electrophilic addition reaction
alcohols are produced industrially by hydrating alkenes in the presence of an acid catalyst e.g. sulfuric acid
alkenes also undergo addition with hydrogen halides
if the HBr adds to an unsymmetrical alkene (propene) there are 2 possible products e.g. 1-bromopropane and 2-bromopropane
e.g. an alkene reacts with hydrogen bromide to form bromoalkanes
electrophilic addition opens up double bond e.g. bromine
3) the other carbon becomes positive and the negative Br bonds forming 1, 2-dibromoethane
2) heterolytic (unequal) fission of Br2. the closer Br gives up electrons to the other Br and attaches to the carbon atom
1) the double bond repels the electrons in Br2, polarizing it (one becomes delta positive, one Br becomes delta negative
electrophilic addition reactions happen to alkenes
electrophiles= electron- pair acceptors, molecules which don't have enough electrons so are attracted to areas with lots of electrons
2) electrophilic addition reactions happen because the double bond has lots of electrons and is easily attacked by electrophiles
1) double bonds open up and atoms are added to carbon atoms
bromine water
bromine reacting with an alkene is an example of electrophilic addition
tests for unsaturation, saturated compounds (alkanes) wont react so solution will stay orange
adding bromine across the double bond forms dibromoalkane
when you shake an alkene with orange bromine water the solution decolourizes
adding hydrogen to C=c bonds produces alkanes
it is an addition reaction because only ONE product is made
ethene will react with hydrogen to form ethane but requires a catalyst e.g. platinum and nickel
alkenes join up to form addition polymers
n= the number of repeating units
brackets= repeating unit
addition polymerization
the double bonds can open up and join together to form a polymer
fuels
many organic compounds burn completely to give CO2
when an alkane is burnt completely CO2 and H2O is produced
combustion of organic compounds are exothermic
carbon dioxide is a greenhouse gas
greenhouse gases in the atmosphere absorb infrared radiation emitted by the earth keeping the earth warm- greenhouse effect
burning carbon based fuels increases the amount of CO2 in the atmosphere which causes global warming
greenhouse effect causes ice caps to melt etc
carbon monoxide is produced by incomplete combustion
carbon monoxide is poisonous
bind to same sites as oxygen on haemoglobin molecules in red blood cells
less oxygen can be carried around the body
can cause people to die of eternal suffocation
unburnt hydrocarbons and oxides of nitrogen
both react in the prescence of sunlight to form ground level ozone which is a component of photochemical smog which causes lung damage and respiratory problems
sulfur dioxide
sulfur dioxide dissolves in the moisture in the atmosphere to form sulfuric acid
acid rain can destroy trees, vegetation, kill fish, corrode builidings
particulates
can settle in peoples lungs and can cause decreased lung function and irritation, can cause cardiovascular problems
contributes to global dimming
fossil fuels are non renewable
coal oil and gas are easily extracted and burn to produced lots of energy but are running out
unsustainable
how to handle problems
governments can change laws to reduce pollution
emissions tests on vechiles
higher taxes for pollution
people can change their behavior
fuels of the future
bio fuels
bio fuels are made from living matter in a short period of time
produce CO2 when burnt but the plants absorb CO2 when growing so they are carbon neutral
bio fuels can be made from waste which would otherwise go to landfill
however engines would have to be modified to use fuels with high ethanol concentrations
land would otherwise be used for growing crops- less food
hydrogen
hydrogen can be burnt in a modified engine and water is the only waste product
the method used to extract hydrogen determines how environmentally friendly the fuel is
difficult to transport/ store