Topic 9: Alkanes and haloalkanes Flashcards
what are organic compounds classified into
families or series
functional group of alkanes, alkenes and alcohol
alkanes = c-c
alkenes = c=c
alcohol = OH
define functional group
Functional group –> a group of atoms responsible for the chemical properties of a compound
Types of hydrocarbons
-compound containing hydrogen and carbon atoms only
-Hydrocarbons can be described as straight chained, branched, or cyclical
prefix of alkanes and alkenes depends on the number of carbon atoms
Meth = 1
Eth = 2
Prop = 3
But = 4
Pent = 5
Hex = 6
Hept = 7
Oct = 8
Non = 9
Dec = 10
why does ethene have different properties to ethanol despite their similar structures
different functional group
same homologus series
justify why the following molecules are all part of the same homologous series
different atoms (chain length) but same functional group
forms of representing different compounds
molecular
empirical
general
displayed
structural
skeletal
calculating alkanes
CnH2n+2
calculating alkenes
CnH2n
general formula for cycloalkanes
The formula for cycloalkanes is the same as the general formula for alkenes (CnH2n)
functional groups
-Two compounds would have different functional groups because different atoms are attached to the carbon chain
homogolous series
A homologous series is a group of molecules with the same functional group (chemical properties/atoms) but different number of CH2 groups.
-methanol, ethanol and 1-propanol have different properties because they are part of a homologous series (same functional group) but different chain lengths
what do functional groups affect
properties of a compound and its reactions
alkene
c=c e.g propene
haloalkane
c-x (halogen)
chloroethane
amine
H2N e.g ethylamine
nitrile
c triple bond n
alcohol
OH e.g ethanol
aldehyde
H-C=O e.g ethanal
carboxylic acid
COOH e.g ethanoic acid
ketone
C=O e.g propanone
ether
C-C-O
molecular formula
e.g heptane = C7H16
Ethanol = C2H6O
empirical formula
-propene = C3H6 = C2H3
displayed formula
-shows the arrangement of atoms in a molecule as well as ALL the bonds –> different structures but same molecular formula
structural formula
-Shows how atoms are arranged in a molecule and which functional groups are present
e.g ethanol (alcohol)
Molecular = C2H6O
Structural = CH3CH2OH
e.g 2-chloropropane (alkane)
Molecular = CH7Cl
Structural = CH3CHClCH3
Methanoic acid = HCOOH
Ethanoic acid = CH3COOH
CHO = aldehyde
COOH = carboxylic acid
Methanoic acid = HCOOH
Ethanoic acid = CH3COOH
skeletal formula
-Represents large complex molecules and also different functional groups
how are c bonds represented
lines
what dont you show for skeletal
For skeletal formula you don’t show C-H bonds but can still show hydrogen
root vs prefix
Root = length of carbon chain
Prefix = branching and functional group
suffix of functional groups
alkene ene
haloalkane Ane
alcohol -O
aldehyde al
ketone One
Carboxylic acid Oic acid
amine amine
nitrile nitride
naming alkanes
1) Look for longest unbranched chain of carbon atoms then name it
2) identify the alkyl group attached to longest unbranched chain
3) Number carbon atoms in the main chain to identify side groups
4) Name compound using longest unbranched chain (no in name must take lowest no.
alkyl groups
Akyl groups are alkane molecules minus one hydrogen atom
Methyl – CH3
Ethyl – C2H5
Propyl = C3H7
2 CH3 = 2 methyl groups
what is given the highest priority
The functional group with the highest priority will be the one which gives its suffix to name the molecule
IUPAC
Highest priority:
-Carboxylic acid
-ester
-acid chloride
-amide
-nitrile
-aldehyde
-ketone
-alcohol
-thiol
-amine
-alkene
-alkyne
-alkane
-ether
-alkyl halide
-nitro
Lowest priorty
state 3 characteristics of a homologous series
-same/own general formula
-same functional group
-similar chemical properties
Butane and 2-methylpropane are isomers –> suggest which type and why
chain isomers
-same molecular formula but different chains of carbon atoms which are arranged differently
-different spatial arrangement
define an isomer
isomers are molecules with the same molecular formula but the arrangement of atoms are different
steps to drawing isomers
1) Draw straight chain alkane
2) Usually other isomer is a branched version
what are the two main categories of isomerism
structural isomerism and stereoisomerism
structural isomerism
Structural isomers have different structural formula but same molecular
The three types of structural isomerism are chain, positional and functional group isomerism
stereoisomerism
Stereoisomers have the same structural formula but the 3D arrangement of atoms is different.
The two types of stereoisomers are geometric and optical isomerism
chain isomer
different chains of carbon atoms
position isomer
different positions of the same functional group
functional group isomer
have different functional groups
what is CH2O the empirical formula of
methyl methanoate
explain why the melting point of dodecane is higher than the melting point of straight chain alkane produced by cracking dodecane
-dodecane = longer
-more and stronger van der waals
state the meaning of a fraction
a group of hydrocarbons that have similar boiling points
state the property which allows fractions to be separatedd
different boiling points
outline the essential features of the fractional distillation of crude oil that enable crude oil to be separated into fractions
-temperature gradient
-cooler at top, warmer and bottom
-fractions have diff boiling points
-bp depends on chain length
Name a lab technique that could be used to separate isooctane from a mixture of octane and isooctane
-fractional distillation
-isooctane and octane have diff boiling points
-isooctane is branched so condenses higher up the fractionating column
iso
branched
complete the equation to show the cracking of one molecule of hexadecane to form hexane and cyclopentane only
C16H34 –> C6H14 + 2C5H10
2g mol less =
2 less hydrogens or 2 less of mr
write an equation for the cracking of hexane to form hexene and one other product
C6H14 –> C6H12 + H2
role of fractional distillation and thermal cracking
FD –> separate compounds with similar boiling points
Cracking –> make shorter alkenes
two conditions of thermal cracking
high temp and high pressure
catalyst used in cracking
zeolite
explain why oil companies need to crack suitable heavy fractions
-shorter fractions are more in demand but are in lower supply
saturated vs unsaturated
-Alkanes are saturated whilst alkenes are unsaturated
Saturated = single carbon bonds only (c-c)
Unsaturated = double carbon bonds (c=c)
boiling point of alkanes
-As chain length increases, boiling and melting point increases because number of contact points increases so more/stronger van der waal forces which require larger amounts of energy to overcome
-Straight chains have higher boiling point than branched chains due to more points of contact in straight chains
alkanes and cycloalkanes
Both alkanes and cycloalkanes are saturated hydrocarbons
General formula for alkanes = CnH2n+2
General formula for cycloalkanes = CnH2n
fractional distillation of crude oil
-crude oil is one of the most important naturally occuring raw materials coming from plankton and ancient biomass
-crude oil is a complex mix of hydrocarbons (alkanes)
-crude oil must undergo fractional distillation but also 2 more processes to meet the demand called cracking and reforming
-hydrocarbons with diff boiling points are separated using fractional distillation
purpose of fractional distillation
separate crude oil into fractions based on their boiling points
describing fractional distillation
-fractional distillation relies on the fact that hydrocarbons have different boiling points
-there is a temperature gradient in the fractionating column where it is cooler at the top
-the higher the boiling point the lower down the column
-heavier molecules form and condense at the bottom
issues with fractional distillation
-fractional distillation produces a larger supply of the heavier fraction than needed but a lower supply of the fractions most in demand
-there is a larger supply of longer chains but a greater demand of shorter chains
-cracking can be used to solve this problem
define cracking
Cracking –> converting heavier fractions into more useful smaller ones by breaking down the longer chains
process of cracking in a lab
1) alkane is heated
2) when it is heated it evaporates forming a gas
3) the gas then passes over the hot porcelain chips (solid aluminium oxide) which causes it to crack
4) large alkane then forms smaller alkanes and alkenes
catalyst in cracking
A catalyst can be used during cracking –> Zeolite or Aluminium oxide
A catalyst speeds up rate of reaction by lowering activation energy and provides surface area for reaction to occur
thermal cracking
-alkenes only
-high temperature
-high pressure
-no catalyst
catalytic cracking
-high temperature
-low pressure
-zeolite catalyst used
-motor fuels, aromatic hydrocarbons, cyclic alkanes, branched alkanes
-cheaper
complete combustion of alkanes
-the complete combustion of fuels containing alkanes provided energy to heat homes and to power vehicles
Combustion –> reaction when a fuel with oxygen releases heat energy
Complete combustion –> hydrocarbon + oxygen –> water + carbon dioxide
incomplete combustion
-occurs when oxygen is insufficient
-either CO and H2O produced or C and H2O
explain why incomplete combustion can occur
limited supply of oxygen
suggest a reason why oil companies reform alkanes such as heptane
has more efficient combustion
what is a fuel
substance that produced energy or heat
why do calculations of global warming exclude the effect of water vapour in the atmosphere
water vapour is much less potent greenhouse gas than carbon dioxide
explain how greenhouse gases cause global warming
greenhouse gases absorb and re-emit radiation from the earth
Describe how SO2 and NO2 come to present in the atmosphere and explain how they can damage a limestone building
-SO2 and NO2 is formed when fossil fuels are burnt
-they react with water to form sulfuric acid which reacts with limestone
-limestone and sulfuric acid takes part in neutralisation
show the reaction between ethanethiol and hydrogen gas
C2H5SH + H2 –> C2H5 (useful) + H2S (removed)
global warming
-The main problem with the complete combustion of alkanes is global warming. This is due to increasing concentrations of CO2 in the atmosphere which is a greenhouse gas.
-Greenhouse gases trap the heat radiation from the earth. This results in rising sea levels and melting ice caps
impurities in fuel
Impurities in the fuel:
-sulfur compounds are the main impurities in crude oil
-These need to be removed before the petroleum products are used as fuels
primary and secondary problems of sulfur compounds
-If sulfur compounds were not removed then sulfur dioxide emissions would be produced.
Sulfur dioxide results in the formation of acid rain
A secondary problem of alkane combustion is the production of the pollutants –> Nitrogen oxides, Sulfur oxides and unburnt hydrocarbons
sulfur dioxide
-sulfur is found as an impurity in crude oil and other fossil fuels. It burns in oxygen to form sulfur dioxide
S(s) + O2 (g) –> SO2 (s)
sulfur trioxide
-Sulfur dioxide may be oxidized to form sulfur trioxide:
2SO2 (g) + O2 (g) –> 2SO3 (g)
formation of acidic solutions
-Both Sulfur dioxide and trioxide dissolve in water to form acidic solutions
SO2 (g) + H2O (l) –> H2SO2 (aq)
SO3 (g) + H2O (l) –> H2SO4 (aq)
nitrogen oxides
-The temperature in an internal combustion engine can reach over 2000 degrees, here nitrogen and oxygen combine at high temps to form nitrogen monoxide:
N2 (s) + O2 (g) –> 2NO (g)
formation of nitrogen dioxide
Nitrogen monoxide reacts further forming nitrogen dioxide:
2NO (g) + O2 (s) –> 2NO2 (g) + CO2 (g)
formation of nitric acid
Nitrogen dioxide gas reacts with rain water and more oxygen to form nitric acid which contributes to acid rain:
4NO2 (g) + 2H2O (l) + O2 (g) –> 4HNO3 (aq)
removal of impurities in fuels
-sulfur impurities can be removed from the crude oil by mixing it with hydrogen and passing it over a hot catalyst
-Any sulfur compounds that are present react with hydrogen to form hydrogen sulfide and a hydrocarbon
Or Removing sulfur from coal before it is burnt is not practical so acidic sulfur oxides are removed from the water gases using a base such as calcium oxide
why are radicals extremely reactive
radicals have unpaired electrons and therefore react quickly in order to gain a pair of electrons once again
explain which part of the earth’s atmosphere will have the highest concentration of radicals
-stratosphere will have the highest concentration of radicals
-UV light filtered via ozone layer
-trosophere recieves less UV
-UV required for initiation
alkanes can undergo substitution reactions
- Alkanes can undergo substitution reactions
e.g CH4 + Cl2 –> CH3Cl + HCL
Alkane + halogen –> haloalkane + hydrogen halide
define substitution reaction
reactions in which one atom in a molecule is replaced by another atom or group of atoms
We can recognize substitution reactions as having two reactants and two products. If only one product is formed and no element replaces the other then it is not a substitution reaction
substitution into alkanes
-alkanes can react with chlorine and bromine. This reaction can happen when they have been heated or if they have been exposed to UV light
e.g CH4 + 2CL2 –> CH2Cl2 + 2HCl (methane –> dichloromethane)
-hydrogen atoms in alkane replaced by halogen atoms
-multiple products can be formed
-For every one H atom that is replaced, one halogen molecule is used and one haloalkane is formed
equation - substitution
CnH2n+2 + X2 –> CnH2n+1X + HX
chloromethane –> dichloromethane
CH3Cl + Cl2 –> CH2Cl2 + HCl
halogenation of alkanes
-the halogenation of alkanes takes place through a radical substitution reaction
-all radical reactions take place involving radicals and three distinct steps
radicals
Radicals –> atoms, molecules or ions that have an unpaired outer electron. They tend to be extremely reactive
Radicals = element or compound with a dot
steps for halogenation of alkanes
1) initiation
2) propagation
3) termination
UV light + homolytic fission
-producing free radicals (initiation) requires UV light or heat
-covalent bonds involve a shared pair of electrons between atoms and therefore the UV light provides energy to break these
-this bond breaks homolytically by homolytic fission in the presence of UV light
initiation
-formation of radicals is not energetically favourable, it requires a large amount of energy. Radicals cannot form in the dark as the molecules do not have enough energy for the bonds to break when they collide
-2 free radicals produced
Molecule –> radical + radical
propagation
-Radicals go on to react as they are highly reactive and need to gain paired electrons
Original radical + molecule –> new radical + molecule
-1 free radical produced
-propagation can occur in multiple steps and the reaction would continue until either all Cl2 is used up or all of the CH4 is used up
termination
-radical based reactions must come to an end and this happens through a process called termination
-termination reactions release large amounts of energy and is exothermic reaction
-0 free radicals produced
Radical + radical –> molecule
testing for alkenes
bromine water
brown –> colourless
cracking
Cracking involves breaking C–C bonds in alkanes.
rotation
double carbon bonds cant usually rotate but single carbon bonds can
structural isomers chemical vs physical properties
chain = same chemical, different physical (boiling point)
Positional = diff chemical and physical
Functional = similar chemical and physical
C=O
ketone
state the property of SO2 that causes pollution when it enters rivers
Give an equation to show the reaction of SO2 with water
-acidic
SO2 + H2O –> H2SO3
explain why cyclohexane would not be a suitable solvent to extract the iodine from the aqueous layer
-it would react with iodine
-it is unsaturated
state the meaning of the term fraction
mixture of compounds with similar boiling points
give one reason why CO2 absorbs infrared radiation
C=O bonds are polar
state on evironmental problem that No caues and what is used to remove it
-acid rain
-catalytic converter
state what is meant by the term carbon neutral
no net emissions of CO2
state why the rates are different
-iodide ions produced more rapidly than bromide ions as C-I is weaker than C-Br
explain how your answer suggest that the alchohol is butan-1ol
-incomplete combustion os experiment must be less exothermic
state why the C-Cl bonds are polar
different electronegativies
Cl = more electronegative
describe the hydrogen bonding in propan-1-ol
-attraction between O lone pair and H+ on another molecule alcohol group
formation and breaking of a covalent bond
the formation of a covalent bond is shown by a curly arrow that starts from a lone electron pair or from another covalent bond
the breaking of a covalent bond is shown by a curly arrow starting from the bond.
E-Z isomerism
E–Z isomerism is a form of stereoisomerism and occurs as a result of restricted rotation about the planar carbon–carbon double bond.
cracking
Cracking involves breaking C–C bonds in alkanes.
highest priority
takes the suffix (end) and lower priorities take the prefix (beginning)
Carboxylic acids >aldehydes>ketones>alcohols>alkenes>halogenoalkanes
alcohol = hydroxy prefix
aldehyde
An aldehyde’s name ends in –al
It always has the C=O bond on the first carbon of
the chain so it does not need an extra number. It is
by default number one carbon on the chain
homolytic fission
each atom gets one electron from the covalent bond
alkene isomers
Alkenes can exhibit a type of isomerism
called E-Z stereoisomerism
why do stereoisomers arise
(a) There is restricted rotation around the C=C double bond.
(b) There are two different groups/atoms attached both ends of the
double bond.
soot
global dimming and respitory problems
greenhouse gases
Carbon dioxide (CO2
), methane (CH4
) and water vapour (H2O) are all greenhouse gases
greenhouse effect
UV wavelength radiation passes through the atmosphere to the Earth’s surface and heats up Earth’s surface.
The Earth radiates out infrared long wavelength radiation.
The C=O Bonds in CO2 absorb infrared radiation so the IR radiation does not escape from the atmosphere.
This energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed.
why do CO2 levels increased
increased burning of fossil fuels
HCl
always side product when forming products in free radical substitution
homolytic fission
breaking of a covalent bond where each atom recieves one electron
Free radical subsitution of CH3Cl and Cl2
1) Cl2 –> Cl + Cl (radical)
2) CH3Cl + Cl (radical) –> CH2Cl (radical) + HCl
3) CH2Cl (radical) + Cl2 –> CH2Cl + Cl2 (radical)
4) CH3Cl (radical)+ Cl2 (radical) –> CH2Cl2 + HCl
suggest the formulae of 2 bromine containing organic compounds formed when CH2Br2 reacts with bromine
CHBr3
CBr4
true or false - use structural formula for free radical subsitution
true
identify a catalyst used in a catalytic converter
platinum
write an equation to show how nitrogen monoxide is removed from the exhuast gases as they pass through a catalytic convertor
2NO –> N2 + O2
give 2 reasons why boilers are designed to ensure complete combustion
-prevents release of CO
-more energy efficient
suggest how and engineer could demonstrate that the combustion of hexane was incomplete
detect CO gases in exhaust particles
suggest why the product Z has more commerical value than hexane
can be made into polymers
outline the essential features of the fractional disillation of crude oil
-fractions have different boiling points
-boiling point depends on chain length
-temperature gradient
-larger molecules with higher boiling points at the bottom
why are alkanes unreactive
-same electronegativity (non-polar)
-strong bonds that require energy to break
shapes of alkenes vs alkanes
alkenes = tetrahedral
alkanes = trigonal planar
write two equations to show how chlorine atoms catalyse the decomposition of ozone
- Cl (radical) + O3 –> ClO (radical) + O2
- ClO (radical) + O3 –> 2O2 + Cl (radical)
explain why bromine, a non-polar molecule is able to react with propene
electron dense C=C causes induced dipole in Br2
electron pair donor vs acceptor
donor = nucelophile
acceptor = electrophile
state and explain the role of the cyanide ion above
nucelophile since it is an electron lone pair donor
name two reagents which could react to form ethanol
-chloroethane
-aqueous sodium hydroxide
state the organic product from a hot concentrated solution of sodium hydroxide in ethanol is added to bromoethane
ethene
organic product when a warm dilute solution of KOH (aq) is added to 2 chloropentane
pentan-2-ol
organic product when saturated ethanolic KOH is added to 2-iodobutane
but-1-ene and but-2-ene
2-bromopentane can undergo elimination to form an alkene. Name the reagents for this reaction
hot ethanolic potassium hydroxide
what type of reaction is nucleophilic subsitution
hydrolysis
what type of reaction is electrophillic addition
hydrogenation
define a haloalkane
an alkane where one or more hydrogens are replaced by a hydrogen
prefixes of halogens
Fluorine – fluoro-
Chlorine – chloro-
Bromine – bromo-
Iodine – iodo-
primary, secondary, tertiary haloalkanes
The terms primary, secondary and tertiary can be used with haloalkanes to describe the position of the functional group e.g primary haloalkane = halide attached to 1 carbon atom
haloalkane synthesis
haloalkanes can be formed by alkenes and alkanes
free radical subsituion and electrophillic addition
1) Free radical substitution (CH4 + Cl2 –> CH3Cl + HCl) or 2)
electrophillic addition (C2H4 + HBr –> C2H5Br)
what are the two ways of forming haloalkanes
Free radical subsitution = alkanes to haloalkanes
Electrophillic addition = alkenes to haloalkanes
chemical reactions of haloalkanes
-C-X bond is polarised meaning the carbon is slightly electron deficient and will have a partially positive charge
Nucleophilles will attack regions with a partially positive charge
The carbon-halogen bond in halogenoalkanes is polar bc all halogens are more electronegative than carbon
nucelophilles
Nucleophiles -> a species with a lone pair of electrons that is attracted to regions of positive charge (NH3, OH, CN)
NH3 = ammonia
OH = hydroxide
CN = cyanide
nucelophilic subsitution of haloalkanes
-nucleophiles attack the carbon of a carbon-halogen bond because the lone pair on the nucelophille is attracted towards the partial positive charge in the carbon
1) Electrons in C-X bond are repelled as the nucleophile approaches the carbon atom
2) The nucleophile bond breaks to the carbon and the C-X bond breaks. Two electrons move to halogen forming a halide ion
-2 products formed
nucelophillic reaction with water
-cold water slowly hydrolyses halogenalkanes replacing the halogen atoms with an OH group to form an alcohol
-if NaOH is used as the nucelophille an alcohol will form with the same mechanism as water
nucelophillic subsituiton by cyanide ions
-cyanide (CN) acts as a nucelophille which increases the length of the carbon chain
-there is a triple bond between the C and N atoms in a cyanide molecule
-lone pair is on the carbon atom
-A nitrile is formed when cyanide is the nucelophile
naming a nitrile
-when naming a nitrile add 1 carbon e.g if reactants is bromoethane then propanitrile will be formed
nucelophillic subsitution by reaction with ammonia
-if we warm a haloalkane with a concentrated solution of ammonia in ethanol a new product is formed
-amine is formed e.g ethylamine (C2H5NH2)
-test tube must be sealed so gases don’t escape
1) the ammonia will attack the partially positive C atom on the haloalkane
2) a secondary molecule of ammonia removes additional hydrogen from one product to form ammonium salt
NH4X and RNH2 = products e.g ammonium chloride (NH4Cl) and ethylamine (CH3NH2) from chloroethane and ammonia
naming products
1) NaOH and 1-chloropropane = propan-1-ol and sodium chloride
2) 1-iodobutane and potassium cyanide = pentanitrile and potassium iodide
3) chloroethane and ammonia = ethylamine and ammonium chloride
4) potassium hydroxide and 2-bromobutane = butan-2-ol and potassium bromide
5) KCN and CH3Cl = potassium chloride and ethanitrile
Aqueous NH3 = heat and pressure
KCN (aq) = nucleophillic substitution
KOH (aq) = nucelophillic substitution
other haloalkane reactions
-When aqueous potassium hydroxide is reacted with a halogenoalkane an alcohol is formed due to nucelophilic subsitution where OH acts as a nucelophile
-However, when hot ethanolic potassium hydroxide is reacted a different reaction occurs
hot ethanolic acid
Hot ethanolic acid = haloalkane + OH- –> alkene + water + halide ion
OH- ion acts as a base in this reaction
temperature, concentration, solvent
Temperature = hotter temperatures favour elimination whereas subsitution is warmer conditions
Concentration = dilute KOH favours substitution whereas elimination favours concentrated KOH
Solvent = Aqueous solutions of KOH in substitution whereas KOH dissolved in ethanol favours elimination
role of hydroxide ions in subsitution vs elimination
In substituion hydroxide ions act as a nucelophile (electron donor) but in elimination hydroxide ions act as base since they accept a proton
Elimination products
-occasionally, a mixture of structural isomers may be formed as H can be eliminated from either side of the double bond
-longer chain = greater mixture of products
g double bond can form on 1st or 2nd carbon
Haloalkanes undergo elimination in the presence of concentrated strong base such as KOH or NaOH in ethanol. An alkene is formed along with water and a halide ion
what can haloalkanes by hydrolysed into
haloalkanes can be hydrolysed in the presence of Oh- to form an alcohol
Haloalkanes react with water to form an alcohol and a hydrogen halide. The water causes the C-X bond to break do reaction is a hydrolysis reaction
-the rate at which hydrolysis occurs is different for different halogenoalkanes
RX + H2O –> ROH + H+ + X-
end product of hydrolysis
The end product of the hydrolysis reaction forms a hydrogen halide (Cl = white Br = cream I = yellow)
Test for presence of a halide = silver nitrate
-if the precipitate appears quickly, hydrolysis is rapid
-if the precipitate takes a long time to appear, hydrolysis is slow
investigating rates of hydrolysis
-rate of hydrolysis of different primary haloalkanes can be investigated by warming each haloalkane with ethanol and then adding warm silver nitrate solution
1-iodopropane reacts the fastest
1/time
C-X bond enthalphy decreases down the group, so does bond strength
thermal vs catalytic cracking
Thermal cracking takes place at high pressure and high temperature and produces a high percentage of alkenes (mechanism not required).
Catalytic cracking takes place at a slight pressure, high temperature and in the presence of a zeolite catalyst and is used mainly to produce motor fuels and aromatic hydrocarbons (mechanism not required).
why can sulfur dioxide be removed from flue gases using calcium carbonate or calcium oxide
We can remove sulfur dioxide by reacting with calcium oxide or calcium carbonate. This is because sulfur dioxide is acidic and calcium oxide is basic.
what bonds do haloalkanes contain
polar bonds
why is UV light needed
provides energy to break the covalent bond in chlorine
what does ozone absorb
UV radiation
CFCs
Ozone, formed naturally in the upper atmosphere, is beneficial because it absorbs ultraviolet radiation.
Chlorine atoms are formed in the upper atmosphere when ultraviolet radiation causes C–Cl bonds in chlorofluorocarbons (CFCs) to break.
Chlorine atoms catalyse the decomposition of ozone and contribute to the hole in the ozone layer.
equation for ozone decomposition
Cl* + O3 → ClO* + O2
and ClO* + O3 → 2O2 + Cl*
suggest one reason other than the use of mean bond enthalpies, why a value for the enthalphy of combustion of a liquid alkane is different to the value obtained
alkane is not gaseous
what statement is correct about the production and use of ethanol as biofuel
biofuel ethanol is purified by fractional distillation
stereoisomer and structural isomers of C4H8
stereo = Z-but-2-ene
chain = but-1-ene and methylpropene
positional = but-2-ene
functional = cyclobutane
which statement is not correct about ozone
its decomposition is catalysed by chlorine molecules
combustion of alkanes
burn with a blue flame
combustion tends to be less complete as number of C atoms increases (stronger van der waals) so will be a smoky yellow flame
chlorination of alkanes
free radical subsitution
ozone layer =
blocks UV light
Cl. + O3 –> ClO. + O2
ClO- + O3 –> Cl. + 2O2
are haloalkanes soluble
no insoluble in water
R group is non-polar
C-F = most polar
test for HBr
ammonia = NH4Br = white fumes
making haloalkane
C6H14 + Br2 –> C6H13Br + HBr
explain with the aid of equations, why a single radical can cause the decomposition of many molecules of ozone
radical = Cl ;
Cl; + O3 –> ClO; + O2
ClO; + O3 –> Cl; + 2O2
Cl radical is regenerated causing the decomposition of the ozone
nucleophilic subsitution =
excess NH3
forming 2 chloro-butane from free radical subsisution =
ensure radical goes on 2nd carbon
