chap 4- the ozone story Flashcards
what happens to the atmosphere the higher you go
becomes less dense
how do you calculate the % composition from the air sample in ppm
divide the ppm by 1,000,000 and then x this answer by 100 to get the %
concentration of 1% is = to 10,000
how do you calculate the sample of air in ppm from % composition
x the percentage by 10,000
when did oxygen begin to collect in the atmosphere
oxygen was first introduced into the atmosphere when the first simple plants appeared and started to photosynthesise but it was used up by oxidising sulfur and iron compounds and other chemicals in the earth’s crust. it started to collect in the atm when this process was largely complete
how does he sun cause cancer
part of the electromagnetic radiation radiated by the sun corresponds to the energy required to break chemical bonds (including those in molecules of DNA)
how does the sun cause people to look wrinkled
sunlight can damage the proteins within skin
why is it possible to burn in water but not through glass
glass lets through visible light but absorbs high energy ultraviolet radiation but water lets through some ultraviolet
why is ozone at ground level in the troposphere a significant pollutant
because it is involved in reactions producing photochemical smog that causes haziness and reduced visibility and irritation and respiratory problems
why is there no life in the stratosphere
the high energy UV radiation would break down the delicate molecules of living things
what is the value for the speed of light
3.00 x10^8 m s -1
what is an equation for calculating the speed of light
wavelength (m) x frequency (s-1)
what is the equation for calculating the energy of a photon (J)
planck constant (Js) x freq (s-1)
what are the different aspects of a molecule’s behaviour
translation (molecule moving around as a whole)
rotation (of the molecule as a whole)
vibration of the bonds
electron energy
what 3 electronic changes can occur when molecules absorb UV radiation
1) electrons may be excited to a higher energy level
2) if higher energy radiation is used the molecules may absorb so much energy that electrons can no longer bond together (photodissociation) and radicals are formed
3) with very high energy photons the molecules acquire so much energy that the electron can leave and so the molecule is ionised
what is heterolytic fission
both of the shared electrons go to just one of the atoms when the bond breaks. this atom becomes negatively charged and the other positively charged
what is homolytic fission
one of the 2 shared electrons goes to each atom so the atoms don’t have an overall charge
how is ozone (O3) formed
when an oxygen atom reacts with a dioxygen molecule
what is the pauling scale
used to measure electronegativity
electronegativity increases up the group and to the right of the period (so the closer you get to fluorine)
when do electrons sit midway between the 2 nuclei
if both atoms have similar or identical electronegatives (the bond is non polar) so the electrons are equally attracted to both nuclei
what is a dipole
a difference in charge between 2 atoms caused by a shift in electron density in the bond
why isn’t CO2 a polar molecule even though it has polar bonds
because the 2 polar bonds are arranged so that they point in opposite directions so cancel each other out
define electronegativity
the ability of an atom to attract the bonding electrons in a covalent bond
how do instantaneous dipole induced dipole bonds cause all atoms and molecules to be attracted to each other
electrons in the charge cloud are constantly moving which forms temporary or instantaneous dipole. this can induce another temp dipole in the other direction on a neighbouring atom. The 2 atoms are then attracted to each other. This can induce another dipole in a 3rd atom and acts like a domino effect
why does a longer carbon chain result in a stronger instantaneous dipole induced dipole bond
there’s more molecular surface on a longer chain so more electrons can interact so requires more energy to overcome the instantaneous dipole induced dipole bonds
why do branched chain alkanes have fewer instantaneous dipole induced dipole bonds
they can’t pack closely together and so their molecular surface contact is small compared to straight chain alkanes of similar molecular mass so fewer instantaneous dipole induced dipole bonds can form
what kinds of atom or molecule have stronger instantaneous dipole induced dipole bonds
larger as they have larger electron cloud so stronger I.D.I.D.B
also molecules with a larger surface area as they have a bigger exposed electron cloud
what is a permanent dipole permanent dipole bond
the partially + and partially - charges on polar molecules can cause weak electrostatic forces of attraction between molecules which are called permanent dipole permanent dipole bonds
what does hydrogen have to bond to in order to form a hydrogen bond
fluorine, nitrogen or oxygen
what is the strongest type of intermolecular bond
hydrogen
why are substances that form hydrogen bonds soluble in water
because they can form hydrogen bonds with the water molecules allowing them to mix and dissolve
why do butan-1-ol and butan-2-ol have different boiling points even though they both form one hydrogen bond per molecule
because of the strengths of the instantaneous dipole induced dipole and butan-1-ol is less branched than butan-2-ol so surface contact is greater so forms stronger instantaneous dipole induced dipole bonds and so butan-1-ol has a higher boiling point
why is ice less dense than water
because in ice the water molecules are arranged so there is a max number of H bonds- a lattice structure is formed and ‘wastes’ lots of space but when ice melts to water some of the H bonds are broken and the lattice breaks down
what 2 things need to happen in order for a reaction to take place between 2 particles
1) they need to collide in the right direction (facing each other the right way)
2) they need to collide with at least a certain amount of kinetic energy
what is activation energy
the minimum amount of energy particles need to react
what are 5 methods that can be used to measure rate of reaction
- measuring vol of gas produced
- measuring loss of mass as a gas is produced
- measuring change in pH during a reaction
- measuring temp change
- taking samples at regular intervals and analysing them by titration
how do chlorine radicals form in the stratosphere
UV radiation breaks the C-Cl bond in CFC’s by homolytic fission
what is the most important factor in determining the relative reactivity of haloalkanes
bond enthalpy
what is the most electronegative element
fluorine (4.0)
why do larger molecules have stronger instantaneous dipole induced dipole bonds
because they have larger electron clouds and a greater surface area which means stronger IDIDB because a larger exposed electron cloud
what happens if you put an electrostatically charged rod next to a jet of a polar liquid (like water)
the liquid will move towards the rod because polar liquids contain molecules with permanent dipoles so it doesn’t matter if the rod is positively or negatively charged because the polar molecules in the liquid can turn around so the oppositely charged end it attracted towards the rod
why are substances that form hydrogen bonds also soluble in water
because they can form hydrogen bonds with the molecules in the water allowing them to mix and dissolve
why do molecules with greater surface contact have higher boiling points
because the molecules can pack closer together and so form stronger instantaneous dipole induced dipole bonds
how can you use evaporation of a substance to investigate what type of intermolecular bonds it’s likely to form
the weaker the intermolceular bonds in a liquid the faster the evaporation rate so a greater temp change observed in a given time
the smaller the temp change the stronger the intermolecular bonds
how does a homogeneous catalyst speed up a reaction
forms one or more intermediate compounds with the reactants. Then the products are formed from the intermediate compounds. The activation enthalpy needed to form the intermediates is lower than that needed to form the products directly
why does an enthalpy profile of a reaction with a homogeneous catalyst have 2 humps
the first hump is the activation enthalpy for the first step (forming the intermediates) and the second hump is the activation enthalpy for forming the products from the intermediates
what is a haloalkane
an alkane with at least one halogen atom in the place of a hydrogen atom
why does the boiling point of haloalkanes increase down group 7
because as you go down group 7 the atomic radius of the halogen atoms and the number of electron shells increases which leads to stronger instantaneous dipole induced dipole forces between molecules
what is a nucleophile
an electron pair donor
donates an electron pair to somewhere without enough electrons
how does a nucleophile react with a haloalkane
because the carbon-halogen bonds are polar and the electronegative halogen pulls electron density away from the carbon so the carbon is electron deficient and can be attacked by a nucleophile
what is a substitution reaction
when a functional group is replaced by another functional group
how does warming a haloalkane with water result in nucelophilic substitution
the partially positive C attracts a lone pair from the O in H2O and the C-Br bond breaks
An intermediate forms with O that has 3 bonds this is unstable so one O-H bond breaks
An alcohol forms
how do haloalkanes react with ammonia to form amines
warm a haloalkane with excess ethanolic ammonia (ammonia dissolved in ethanol) the ammonia swaps places with the halogen and an amine is formed
what is an amine
organic compounds based on ammonia but one or more of the hydrogen atoms are replaced by alkyl groups
what is the most reactive haloalkane
iodoalkanes
what is an experiment to test the reactivity of haloalkanes
put a chloroalkane, a bromoalkane, and an iodoalkane in 3 different test tubes. add some silver nitrate solution and some ethanol.
The silver nitrate halide is insoluble so forms a precipitate but the precipitate forms fastest with iodoalkane so must be the most reactive and slowest with chloroalkane
what are the 3 main stages of a radical chain reaction
1) initiation- free radicals are produced
2) propagation- free radicals react with molecules and produce new radicals. these go on to react with more molecules producing more radicals (the chain part)
3) termination- two radicals react together to form a stable molecule
how are haloalkanes formed
when a halogen reacts with an alkane in a photochemical reaction (reaction started by light)
a H atom is substituted by Cl or Br (a radical chain reaction)
how is ozone formed
if the right amount of UV radiation is absorbed by an O2 molecule, it splits into free radicals which them combine with O2 molecules to form ozone
how is the ozone layer continuously replaced and destroyed
as UV radiation hits O3 molecules it forms O + O2 and an equilibrium is set up as a reversible reaction
why is the ozone layer so important to us
when it breaks down it absorbs high energy UV radiation- removes all UVC radiation and 90% of UVB which are harmful to humans and other life on earth
how does ozone occur at ground level
in the troposphere due to the effect of sunlight on NO2 and hydrocarbons (mainly from vehicle engines and power stations)
how is photochemical smog formed
when ozone mixes with solid particles of carbon and other substances. this can cause respiratory problems and is toxic to humans
what is a chlorofluorocarbon
haloalkanes that have all their hydrogen atoms replaced by chlorine and fluorine atoms
what is the most likely carbon- halogen bond to be broken by UV radiation
the carbon-iodine bond because it has the lowest bond enthalpy and the carbon-fluorine is least likely as it has the highest bond enthalpy
what 2 types of free radicals can destory ozone
1) NO from nitrogen oxides
2) any halogen free radicals from haloalkanes
what are quantised energy levels
the fixed energy levels in molecules that electrons can jump between
why do molecules only absorb specific frequencies of radiation
because the energy needed for an electron to jump to the next energy level is quantised
how do you calculate the energy from radiation
E (J) = h (planck’s constant) x v (freq in Hz)
how do you calculate the wavelength of radiation
wavelength = speed of light / freq in Hz
what is an overall equation for calculating energy from radiation wavelength
E= hc/ wavelength E= planck x speed of light (ms-1) / wavelength (m)
what are 2 features of a water molecule than enable it to form hydrogen bonds
1) the lone pair of electrons on the O atom making it electronegative
2) hydrogen with partially + charge
why does bromomethane have a higher boiling point than chloromethane
because bromomethane imf are stronger than chloromethane caused by more electrons and a bigger molecule
