The Ozone story - Unit 4 Flashcards
What happens to the atmosphere the higher up you go?
It becomes less dense
What are the two most important parts of the atmosphere and there order?
1 - Troposphere
2 - Stratosphere
What does 339 ppm of N2 mean?
Out of one million particles in a sample of air, 336 will be N2 particles
How do you convert percentage to ppm?
x 10,000
What is the main source of anthropogenic CO2 emissions? (2)
1 - Combustion hydrocarbon fuels
2 - Deforestation
What is the main source of anthropogenic Methane emissions? (4)
1 - Cattle farming
2 - Landfill sites
3 - Rice paddy fields
4 - Natural gas leakage
What is the main source of anthropogenic Nitrous Oxide emissions?
1 - Fertalised soils
2 - Changes in land use (e.g from soil when land is ploughed)
What is the main source of anthropogenic Carbon Monoxide emissions?
1 - Incomplete combustion of hydrocarbosn - car exhausts
What is the main source of anthropogenic Nitrogen Oxides emissions?
1 - Internal combustion engines e.g from reaction of N2 and O2 at high temps
What is the most damaging type of electromagnetic radiation to the skin?
Ultraviolet
What is a positive effect of Ozone in the atmosphere?
1 - In the stratosphere, ozone absorbs high energy UV radiation
What are the damaging effects of UV radiation? (3)
1 - Damage DNA leading to skin cancer
2 - Damage eyes leading to cataracts
3 - Damge crops
What are the negative effects of Ozone in the atmopshere? (3)
1 - In the troposphere, is a pollutant
2 - Involved in reactions that produced photochemical smogs
3 - This causes: Reduced visability, respiratoty issues
Is the speed of light differnet for different elcrtomagntic raditaion?
No, it’s a constant
What is a key feature of electronic, rotational, translational and vibrational energy?
1 - All the types of energy are quantised, has a definite amount of energy
2 - This means they all occupy definite energy levels
What are the effects of infared radiation on your body? (2)
1 - Makes bonds in the chemicals in your skin vibrate more energetically
2 - The molecules have more kinetic energy resulting in you feeling warmer
What type of electromganetic radiation do, electronic, vibrational and rotational energy levels absrob?
Electronic - Visable + UV
Vibrational - Infared
Rotational - Microwave
Out of electronic, vibrational, rotational and translational energy changes, what requires the most energy and why?
1 - Electronic - Energy levels furthest apart
2 - Vibrational
3 - Rotational
4 - Translational
What are the three things that can happen when a Cl2 absorbs radiation?
1 - e- excited to higher energy level and energy released
2 - If higher energy photon absorbed - Photodissociation occurs - bonding e- can no longer bond the atoms together, forming a radical Cl
3 - If very high enery photon absorbed - Ionisatoion - e- is able to leav molecule
What are radicals?
1 - Molecules or atoms with atleast on unpaired e-
2 - Very reactive so can lead to further reactions
What’s another word for bond breaking?
Bond fission
What is heterolytic fission? (2)
1 - Both of the shared e- go to just one atom when the bond is broken
2 - This atom then becomes negativly charged because it has one more e- than proton and the other atom becomes positivley charged
What is homolytic fission?
The breaking of a covalent bond in which each bonding atom receives one electron from a bonding pair, forming two radicals
How are radicals most commonly formed?
When the bond being broken is non - polar
What conidtions increase the likliehood of a polar bond being broken by homolytic fission (2)
1 - Reaction taking place in the gas phase
2 - Presence of light
In homolytic fission, what can happen to the unpaired e- on the radicals? (2)
1 - The unpaired e- can be ommited and the radical represented as Br instead of Br.
5 - The unpaired e- has a strong tendency to pair up with another e- from another substance
How can Oxygen radical be formed?
The photodissociation of dioxygen molecules when UV radiation of the rigth frequencey is absorbed
What is a polar bond and when does it form? (2)
1 - Where one atom is slightly + and the other slightly -
2 - Happens when atoms have a different electronegativity
Why are radicals reactive?
They try to fill their outer shells by grabbing an e- from another atom or molecule
What does a full headed curly arrow represent?
The movemnet of a pair of e-
What does a half headed curly arrow represent?
The movemnet of a single e-
What is formed in the reaction between Methand and Chlorine?
1 - HCl
2 - Chloromethane
3 - Ethene
4 - Further substitution can form dichloromethane and trichloromenthane
What is a radical?
(molecules or atoms) with an unpaired electron
What is steady state?
Something is being made as fast as it’s being used up
How could you measure a colour change in a reaction?
Using a colorimeter
What is the equation for rate of reaction?
change in property
time taken
What is chemical analysis and what are it’s downfalls?
1 - Taking samples of the reaction mixture at intervals and quenching them (stopping the reaction int the sample). the samples are then analysed
2 - This interferes with the progress of the reaction
What factors affect the rate of reaction? (6)
1 - Catalyst
2 - Concentration of reactants
3 - Temp
4 - Pressure
5 - SA of reactants (particle size)
6 - Intensity of radiation
What is Activation enthalpy?
The minimum kinetic energy required by a pair of colliding particles before a reaction will occur
What is the transition state in an enthalpy profile?
The highest point on the pathway from reactants to products, where old bonds stretch and break and new bonds start to form
What is the effect of a temp rise of 10oc on rate reaction?
Doubles rate of reaction
What does the Boltzmann distribution curve show?
Distribution of molecular energies.
Why do reactions go faster at higher temperatures?
because a larger proption of the collding molecules have the minmum Ea needed to react
What is the relationship between Ea and the effect raising the temp has on a reaction?
The greater the Ea , the greater is the effect of increasing the temperture on the rate of reaction
Why do reactions go faster when using a catalyst? (2)
1 - Provide an alternative reaction pathway with a lower Ea
2 - Therefore, there is a larger proportion of particles that on collsion produce a sucessful collison
What does the dot represent B.?
The unpaired e-
What is an easy way of deciding whether or not something is a radical?
If then no. of e- shells is odd then it is a radical
What are the stages of a free radical chain reaction?
1 - Initiation
2 - Propogation
3 - Termination
What are the features of an initiation reaction? (3)
1 - One or more molecules react to form radicals
2 - A bond breaks by homolytic fission so the reaction is endothermic
3 - Often happens in the presence of uv light
What are the features of a propogation reaction? (3)
1 - A molecule and a radical react to form a new molecule / radical
2 - A bond breaks and a new bond forms
3 - Propagation reactions usually occur in pairs
What are the key features of a termination reaction? (2)
1 - Two radicals react to form one molecule
2 - A bond forms, so the step is exothermic
Write an intitiation equation for Br2?
Br2 → Br● + Br●
Write propgation equations for Br● + CH4, labelling the intermediate radical?
CH4 + Br● → CH3●(intermediate radical) + HBr
CH3● + Br2 → CH3Br + Br●
Write an termination equation for two Br● radicals?
Br● + Br● →Br2
How do you identify an intermdiate radical in a propgation reaction?
Add up the two reactions and the radical that appears on btoh sides are the intermediates
What is CFC?
ChloroFlouroCarbon
What are the features of CFC? (3)
1 - Very strong bonds
2 - These require a very high frequnecy radiation to break bonds
3 - Therefore, CFC very stable in troposphere
Where can a CRC bond be broken and how? (2)
1 - Only in the stratopshere as has high enough frequency radiation
2 - A CRC bond then breaks by homolytic bond fission
Why is NO deplete less O3 than CFC’s?
NO are water soluble wherease CFC’s are not, so NO’s absorb into atmopsheric moisture in the tropopshere so few reach the stratosphere
How can a polar bond produce a non polar molecule?
If the e- are being pulled in equal but opposite directions
What makes a molecule polar?
If the e- are being pulled in similar directions
What is the strenght of the “id,id” effect?
Produces weak intermolecular froces between induced dipole and instantaneous dipole
How does the Enthalpy change compare with a uncatalysed and catalysed reaction?
It is the same
How do catalysts work in a reversable reaction?
They alter the rate at which the equilirium is obtained by not the composition of the equilibirum mixture
What is a homogeneous catalyst and how do they work? (3)
1 - Catalyst in same physical state as reactants
2 - Form an intermediate compound with the reactants (transition state)
3 - The intermediate compound then breaks down to give the product and reform the catalyst
Why does a Cl radical have a more significant effect on O3 depletion than O radicals?
1 - The reaction of Cl. + O3 is much faster than with the O<strong>.</strong>
2 - The Cl atoms are regnerated back into Cl. and go onto react wiht more O3
Are Br radicals or Cl radicals more effective at destroying O3 ?
Br radicals
Are all radicals highly reactive?
No, some are fairly stable
Why does the enthalpy profile for the catlysed reaction have two humps? (3)
1 - Because an intermediate compound is formed with the reactant
2 - The intermediate is then broken down, giving a product and reforming the catalyst
3 - There is therefore two humps for the two steps
What happens to the electronegativity of atoms as you go down a group and why?
1 - Electronegativity decreases
2 - The outer shell is further away from the nucleus, therefore the electrostatic attarction is less between the incoming e- and atom
What happens to the electronegativity across a period?
Increases
Where is the id-id effect present?
In all molecules
What factors reduce the id-id forces?
1 - More branches
2 - Less e-
What does pd-pd stand for?
permanent dipole - permanent diople
What type intermolecular force is stronger , pd-pd or id-id and what does this mean? (3)
1 - pd-pd forces stronger than id-id forces
2 - Therefore more energy is required to overcome the force therefore a higher temp
3 - Therefore molecules with pd-pd forces have a higher bpt and mpt
What is the key thing to rember about the interaction of pd-pd and id-id forces in molecules?
Even if a molecule has pd-pd forces it will always have id-id forces as well
Put hydogrogen bonding, i-id effect and pd-pd effect in order of strength?
1 - Hydorgen bonding - strongest
2 - pd-pd - 2nd strongest
3 - id-id - weak
Can you write id-id or pd-pd in exam?
NO
What is a framework for explaining why a substance requires a higher temp to boil? (4)
1 - In X there are ‘instantaneous dipole - induced dipole’ and ‘permanent dipole- permanent dipole’ intermolecular forces between the molecules
2 - In Y there is also hydorgen bonding due to to the presence of the OH group
3 - Hydrogen bonds are stronger than ‘pd-pd’ interaction
4 - Therefore, Y has stronger intermolecular forces and requires more energy to overcome these forces and therefore requires a higher temp to boil
Is CO2 polar?
No, is non poalar
Between CO2 and SiO2, which one has the highest Bpt? (3)
1 - SiO2
2 - This is because it is a giant covalent structure and therefore contain strong covalent bonds which require lots of energy to break therefore a high temp is needed
3 - CO2 has weak id-id intermolecular forces which require little energy to overcome, therefore a lower temp is needed
What is viscosity a measure of?
How strongly the molecules in the liquid attract each other
When a liquid in a test tube is inverted, what must happen before a bubble can rise?
bonds between molecules must be broken as molecules are forced apart
How do you decide which halogen prefix to put before the alkane?
Alphabetical order
How is a small molecule of the same element held together? (2)
1 - Both nuclei are attracted to the shared e- between them
2 - Both atoms are identical so the e- are shared equally
How are two atoms of different size or group bonded together and what does this cause ? (4)
1 - The smaller atom has a higher electronegativity as it’s nucleus is closer to the shared e-
or
2 - The nuclues with the greater charge has the highest e- so is closer to the e-
3 - This means this atom gets a slight neg charge beause it has a greater proprortion of the e-
4 - This forms a polar bond
When a solid melts or boils what happens? (2)
1 - Intermolecular bonds are broken
2 - However any covalent bonds within the molecule remain intact
What is the boiling point of nobel gases?
low
What is the trend in Bpt of alkanes in relation to chain length? (3)
1 - The longer the chain
2 - The stronger the intermolecular forces
3 - The higher the Bpt
What is the trend in Bpt of alkanes in relaton to braches? (2)
1 - In staright chain alkanes there is more contact between molecules and therefore more opportunities for intermolecular bonds to form
2 - Therefore straight chain alkanes have a higher Bpt than branched isomers
What is a dipole?
A molecule with a pos end and a neg end
What is said when a molecule has a dipole?
The molecule is polarised
When do permanent dipoles occur?
When the two atoms in the bond have a substantial diff between electronegativities
How is it possible for a molecule to not be polar but have polar bonds?
1 - The diples are moving in equal but opposite directions
2 - Therefore the dipoles cancel so there is no overall dipole - the molecule is non-polar
How does an instantenaous dipole form? (3)
1 - In an instant, more of the - cloud is at one end of the molecule than the other
2 - The molecule therefore has an instantanoeus dipole
3 - The e- then change positions, changing the polarity of the molecule
How does an induced dipole form? (2)
1 - When an instantaneous diploe/permanent dipole is next to the unpolarised molecule it can either attract or repel it’s e-
2 - This induces a dipole within the molecule
What is the trend in Bpt of the halogens and why? (2)
1 - Going down the group the molecule are bigger and therefore have more e-
2 - Therefore the ‘id-id’ bonds increase and therefore the melting and Bpt increase
How does HCl reduce the destruction of ozone? (2)
1 - It is a Chlorine reservoir molecule, therefore it stores Cl in the startosphere
2 - This therefore means less Cl is reacting with O3 and removing it
What three features must the molecule involved have in order for hydrogen bonding to take place?
1 - H-N, H-F, H-O bonding to form a large dipole
2 - A small H+ to get very close to O,N or F atoms in the neighboring molecules
3 - A lone pair of e- on the O, N or F which the H+ can line up with
Describe hydrogen bonding in HF? (4)
1 - The H atoms have a strong + charge because they are bonded to the highly electronegtive F atom
2 - The H+ lines up with the lone pair of e- on a neighboring F atom
3 - The H and F atoms get very close because the H atom is so small
4 - Therefore the H and F attract very strongly
What effect does hydorgen bonding have on the viscosity of a substance? (4)
1 - Increases the viscosity because:
2 - When liquids flow the molecule move past eachother
3 - This requires the constant breaking and forming of intermolecular bonds
4 - Therefore, the stronger the bond the harder it is for the liquid to flow - increases viscosity
What affect does hydrogen bonding have on the solubility of a substance?
1 - Makes it soluble in water
2 - This is because hydrogen bonds can form between water molecules and molecules of the substance, helping it dissolve
Explain why water contains more hydrogen bonding than other substances (3)
1 - The O atom contains 2 lone pairs of e- and there are twice as many H atoms as O atoms
2 - This means there are as many hydrogen atoms as lone pairs
3 - Therefore the H+ can line up with the lone pairs, forming many hydrogen bonds
Desrcibe the hydrogen bonding in ice?
There are 4 groups around each O atom therefore the hydrogen bonding between the molecules is maximised
What is a nuclephile?
Something that can donate a pair of e- to form a covalent bond
What feature must a nucleophile have?
1 - Must have a non-bonding pair of e-
What are the reaction conditions needed for the reaction between NH3 nulceophile and a halogenolakane? (4)
1 - Conc. NH3
2 - aqueous
3 - Heat
4 - Sealed tube
What are the conditions needed to make a halogenoalkane? (3)
1 - Hydrogen halide
2 - Conc. sulfuric acid + Na (halide)
or
- Conc. phosphoric acid + Na (halide)
3 - Heat under reflux
Why is ethanol added to the haloalkanes in the experiment ‘How do haloalkanes differ in reactivity’?
Haloalkanes are insoluble in water so the ethanol acts as a mutual solvent for the haloalkane, the water, and the silver ions so they mix together
Breifly describe the experiment for ‘How do haloalkanes differ in reactivity?’ (3)
1 - React a know halogenoalkane with silver nitrate (aq) in the presence of ethanol and time how long it takes to go cloudy
2 - A lower time = More reactive
3 - Bond enthalpy matters more than bond polarity because the bond enthalpy differs more
What are the points needed to include in the Exp. ‘How do haloalkanes differ in reactivity?’ (6)
1 - specified amounts
2 - How to measure e.g graduated pipette, burette
3 - 500c waterbath
4 - When to start timing and stop
5 - Why ethanol used
6 - Silver nitrate used as forms a precipiate with halide
What are Substitution reactions involving water and hydroxide ions are known as?
Hydrolysis reactions
What is a nucelophile?
A molecule or negativley charged ion with a lone pair of e- that it can donate to a poistivley charged atom to form a covalent bond
What is substitution?
A reaction in which one atom or group in a molecule is replcaed by another atom or group
Describe the nucleophillic substituion reaction of 1-bromobutane and OH- ions? (4)
1 - The OH- nucleophile attacks the e- deficient carbon atom in the C-Br bond
2 - The OH- ion then donates 2e- to from a new dative covalent bond with the carbon atom
3 - The C-Br bond breaks heterolytically + the Bromine atom recives 2 e-, producing a Bromide ion.
4 - The Bromine ion is the leaving group
What does heating under reflux mean?
Heating without loss by evaporation
Describe the hydrolyis reaction of 1-bromobutane? (4)
1 - The lone pair of e- on the O atom in the water nucleophile attacks the e- deficient carbon atom in the C-Br bond
2 - The water then donates 2e- to from a new dative covalent bond with the carbon atom
3 - The C-Br bond breaks heterolytically + the Bromine atom recives 2 e-, producing a Bromide ion.
4 - The resulitng ion then loses H+ to form an alchohol and HBr
Describe the nucleophillic substituion of Bromobutane and Ammonia? (4)
1 - The lone pair of e- on the nitrogen atom in the ammonia nucleophile attacks the e- deficient carbon atom in the C-Br bond
2 - The ammonia then donates 2e- to from a new dative covalent bond with the carbon atom
3 - The C-Br bond breaks heterolytically + the Bromine atom recives 2 e-, producing a Bromide ion.
4 - The resulitng ion then loses H+ to form an amine and Hbr
What is the general formula for amines?
R-NH2
Describe the production of a haloalkane from an alchohol? (5)
1 - In the presence of a strong acid:
2 - The Oxygen atom donates a pair of e- to the H+ ion to form a dative covalent bond
3 - This gives the Oxygen atom an overall positive charge
4 - This gives the Carbon atom attached to the Oxygen a higher partial positive charge so it is now more readily attacked by halide ions
5 - Haloaklane + water then formed
What would you expect a poalar bond to do?
The bond would be hydrolysed easier
Watsthe reactivity of fluro compounds?
Unreactive as the C-F bond enthalpy is too high
What was the response to Ozone depletion?
1 - Restricting the release of CFC’s and ozone depleting subatnces into the atomsphere
2 - Finding replcaments for CFC’s e.g HCFC’s as the H-C bonds mean the HCFC’s are broken down in tropsphere
- However, some HCFC’s do make it to stratopshere where they photodissociate to produce Cl radicals - but still have no O3 depleting effect
What effect does a catalyst have on equillibrium?
No effect
