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what is the general formula of alkanes?
CnH2n+2
are alkanes saturated or unsaturated?
saturated
what structure do the covalent bonds around each carbon atom of alkanes form?
a tetrahedral structure
what is the name of the covalent bond within alkanes?
sigma bonds
what are sigma bonds and can they rotate?
overlap of orbitals directly between the bonding atoms, free rotation of the σ-bond
why are alkanes non polar?
because their carbon and hydrogen atoms have similar electronegativities
are alkanes soluble or insoluble within water?
they are insoluble within water
why are alkanes insoluble in water?
they have no permanent dipoles so cannot form hydrogen bonds
why are alkanes generally unreactive?
because of the strong covalent bonds within alkane molecules
what does a longer carbon chain result in?
the stronger the induced dipole dipole interactions
as there is more surface contact
more energy needed to overcome induced dipole dipole interactions
why do branched chain alkanes have lower boiling points than their straight chain isomers?
they have smaller molecular surface areas so induced dipole dipole forces are reduces
what type or reaction is the burning of alkanes?
a combustion reactipn
why must liquid alkanes be vaporised first before they undergo combustion?
combustion reactions happen between gases
so liquid alkanes must be vaporised first
smaller alkanes are more volatile so they burn more easier
define volatile?
turns into a gas more easily
why do larger alkanes make good fuels?
larger alkanes release heaps more energy per mole as they have more bonds to react
what happens when alkanes react fully with oxygen?
they undergo complete combustion to produce carbon dioxide and water
what happens when alkanes react partially with oxygen?
they undergo incomplete combustion producing carbon monoxide and water or carbon particulates and water
what can carbon monoxide (CO) bind to, then prevent?
it binds to haemoglobin before oxygen therefore prevents oxygen from being carried around the body
what is breaking covalent bonds called?
bond fission
state the 2 ways in which covalent bonds can break?
homolytic fission
heterolytic fission
what occurs in heterolytic fission?
the bond breaks unevenly with one of the bonding atoms recieving both electrons from the bonded pair
two different substances are formed, a positively charged anion and a negatively charged cation
what occurs in homolytic fission?
the bond breaks evenly and each bonding atom recieves one electron from the bonded pair
2 electrically uncharged radicals are formed
define radical?
particles that have an unpaired electron
why are radicals very reactive?
because of their unpaired electron
in what reactions do halogens react with alkanes, using what light?
in photochemical reactions using ultraviolet light
what occurs in a free radical substitution reaction?
a hydrogen atom is reolaced by chlorine or bromine
what are the 3 reaction mechanism stages?
initiation reactions
propagation reactions
termination reactions
state the steps of initiation?
uv light provides enough energy to break the covalent bond
homolytic fission occurs
therefore the atom becomes a highly reactive free radical due to its unpaired electron
state the steps of propagation?
a bromine radical reacts with a C-H bond in the alkane
this forms an alkyl radical and a molecule of hydrogen bromide HBr
each alkyl reacts with another bromine molecule
this forms a halogenalkane and a new bromine radical
state the steps in termination?
when two free radicals join together they make a stable molecule
there are any possible termination reactions
what is the general formula of alkenes?
C nH2n
are alkenes saturated or unsaturated?
unsaturated
what 2 bonds is a double bond made from?
a sigma and a pi bond
when is a sigma bond formed?
when 2 s orbitals overlap in a straight line
when is a pi bond formed?
by the sideways overlap of two adjacent p orbitals
why are pi bonds weaker than sigma bonds?
because the electron density is spread about above and below the nuclei so the electrostatic attraction between the nuclei and the shared pair of electrons is weaker
do pi or sigma bonds have relatively low enthalpy?
pi bonds’
what is the shape around the c=c bond in alkenes?
trigonal planar
can c=c double bonds rotate?
no
define stereoisomers?
compounds with the same structural formula but with a different arrangement in space
what are the 2 types of stereoisomers?
E and Z
how are groups positioned in a Z isomer?
has both groups has the same groups either above or below the double bond
how are groups positioned in an E isomer?
has the same groups positioned across the double bond
if the groups of the higher priority are on the same side of the double bond what is the name of the isomer?
if the groups of the higher priority are on the same side of the double bond the compound is the z isomer
if the groups of higher priority are diagonally placed across the double bond what is the name of the isomer?
if the groups of higher priority are diagonally placed across the double bond the compound is the E isomer
what other isomers can E/Z isomers also be called?
cis- trans isomers
define the cis isomer?
has the hydrogen atoms on the same side
define the trans isomer?
has the hydrogen atoms on opposite sides
define electrophile?
electron pair acceptors
what do alkenes react with hydrogen to form?
alkanes
state the conditions needed for alkenes reacting with hydrogen to form alkanes?
Nickel catalyst , hydrogen and high temperatures
what do halogens react with alkenes to form?
dihaloalkanes
what is the name of the reaction when halogens react with alkenes to form dihaloalkanes?
electrophilic addition
what do alkenes react with hydrogen halides to form?
haloalkanes
what can alkenes be hydrated with steam to form?
alcohols
what conditions are needed for alkenes to react with steam to form alcohols?
high temperatures
high pressures
acid catalyst, H3PO4
what can be used to test for alkenes?
bromine water, turns colourless in the presence of alkenes
what is the general formula of alcohols?
CnH2n+1OH
what are the types of alcohols?
primary
secondary
tertiary
what makes alcohols polar?
the electronegative hydroxyl group which pulls the electrons in the C-OH bond away from the carbon atom
as alcohols get larger, does solubility increase or decrease ?
their solubility in water decreases
why does solubility decrease when alcohols increase in size?
in larger alcohols most of the molecule is a non polar carbon chain so there’s less attraction for the polar H2O molecules
what bonds do alcohols form with each other?
hydrogen bonds
why do alcohols have low volatility?
due to their strong hydrogen bonds
in substitution reactions involving alcohols what is the hydroxyl group replaced by, transforming the alcohol into what?
the hydroxyl group is replaced by the halide so the alcohol is transformed into a haloalkane
what takes place in eleimintaion reactions?
water is eliminated from alcohols
what is the oxidising agent which can oxidise alcohols?
acidified dichromate
Cr2O7 2–/H+ (i.e. K2Cr2O7/H2SO
what can primary alcohols be oxidised to form?
aldehydes and then to carboxyllic acids
what can secondary alcohols be oxidised to form?
ketones
what can tertiary alcohols be oxidised to form?
tertiary alcohols cannot be oxidised
under what conditions will a primary alcohol completely oxidise to form a carboxylic acid?
when heated strongly under reflux with excess acidified dichromate
what is the general formula of aldehydes and ketones?
CnH2nO
what functional group do aldehydes and ketones have?
C=O
what do aldehydes have attached to their carbonyl carbon atom?
a hydrogen and one alkyl group
what do ketones have attached to their carbonyl carbon atom?
2 alkyl groups
are electrophiles positively or negatively charged ions?
positively charged ions
define addition polymerisation?
when the double bonds in alkenes open up and join together to make long chains called polymers
why are many polymers difficult to dispose of?
they are not biodegradable
where can waste plastics be buried?
in landfills
why is there a need to reduce landfill?
because the amount of waste we generate is increasing there is a need to reduce landfills a much as possible
state 2 ways in which plastics derived from non renewable oil fractions can be reused?
can be recycled be melting and remoulding them
can be cracked into monomers and used as organic feedstock to make more plastics or other chemicals
why should we be cautious when burning waste plastics?
polymers that contain chlorine e.g PVC produce HCL when burned which needs to be removed
define biodegradable polymers?
polymers which naturally decompose
what can biodegradable polymers be made from?
renewable raw materials such as starch or oil fractions
define photodegradable polymers?
polymers which decompose when exposed to light
define haloalknes?
alkanes with at least one halogen atom in place of a hydrogen
is the carbon halogen bond in haloalkanes polar?
yes
why is the carbon halogen bond in haloalkanes polar?
because halogens are more electronegative than carbon
define a nucleophile?
an electron pair donor, negative ions
what is the name of the reaction when halogens are hydrolysed to alchohols?
nucleophilic substitution reaction
what are the conditions needed to hydrolyse a haloalkane to an alcohol?
a warm aqueous alkali
reflux
what does the speed at which different haloalkanes are hydrolysed depend on?
bond enthalpy
which haloalkanes have the weakest bonds therefore hydrolyse quickest?
iodoalkanes
which haloalkanes have the strongest bonds therefore hydrolyse slowest?
fluoroalkanes