Unit 2 : The Atmosphere

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Diamond Covalent Structure
Each C atom is covalently bonded to 4 other C atoms. Tetrahedral shape, and forms a crystal lattice structure. It's hard. Good thermal conductor as vibrates easily. H.m.p.t. Can't conduct electricity, insoluble in solvents.
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Silicon Oxide
Giant lattice. Covalently bonds with 4 O atoms. tetrahedral shape. Crystal lattice. O atoms only bond with 2 Si atoms. Hard crystalline solid, h.m.p.t. Insoluble in solvent. Doesn't conduct electricity.
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Difference between the structures of CO2 and SiO2.
CO2=small molecules, each C forms double bond with O atoms. Gas @ r.t. as weak i.d-i.d forces. Dissolves in H2O. SiO2=giant lattice. Si atom forms single bonds with 4 O atoms. H.b.p.t. insoluble.
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What affects rate of reaction.
Concn=Particles closer together, collide more -more chances to react. Pressure=Particles closer together, collide more-more chance of reacting. Surface area=More particles come in contact with other reactants, -speedier reaction.
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Activation enthalpy
Minimum amount of kinetic energy particles need to react
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Qualitative effect of temperature changes on rate of reaction
Particles have more kinetic energy, more likely to react when they collide.
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Homogenous catalysts
Form one+ intermediate compounds which the products are formed from. The activation enthalpy needed to form this is lower. It's enthalpy profile will have two humps in it.
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Dynamic equilibrium
The rates of the forward and backward reaction is equal. The concentration of reactants and products are constant. This takes place in an enclosed system.
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Le Chatelier's Principle
If there's a change in concentration, temperature or pressure, the equilibrium will move to help counteract the change.
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Le Chatelier's Principle = Temperature and Concentration
Concn=reactant-shifts to right, makes more product. Product-shifts to left, makes reverse reaction faster. Temp=Increase-shifts to endothermic direction, absorb heat. Decrease-shifts to exothermic direction, replace heat.
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Le Chatelier's Principle = Pressure + Catalysts
Increase=shifts to side with fewer gas molecules, reducing pressure. Decrease=shifts to side with most gas molecules, raises pressure. Catalysts=No effect, can't increase yield-but equilibrium reached faster.
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Gases present in the atmosphere
Nitrogen=78%, Oxygen=21%, Argon=1%, Carbon Dioxide=0.035%. Oxides of N=car engine, Oxides of S=burning fossil fuels, CO=Incomplete combustion of hydroC
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Calculating values for composition in parts per million
% x 10,000
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The depletion of Ozone due to halogenoalkanes
Chlorine free radicals form when CFCs are broken down by UV. Radicals=catalysts, react with ozone to form an intermediate + O molecule. The Cl molecule regenerates, + attacks other ozone molecules. R+O3-->RO+O2, O'+RO-->O2+R
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Heterolytic Fission
2 different substances are formed, a +ve cation and a -ve anion.
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Homolytic Fission
2 electrically uncharged 'radicals' are formed. Radicals have an unpaired electron, thus making them very reactive.
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Initiation reactions
Sunlight gives energy to break the Cl-Cl bond=photodissociation. Bond splits equally, each atom gets 1 electron=homolytic fission. Atom is highly reactive free radical.
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Propagation reactions
Cl' attacks a methane molecule. New methyl free radical attacks another Cl2 molecule. Which attacks a new molecule and so on.
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Termination reaction
If 2 free radicals join together, it makes a stable molecule.
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How did scientists realise the problem caused to the Ozone?
Recent measurements of ozone over Antarctic lower than previous measurements, thought instruments faulty. High-altitude flights in converted spy plane, satellite data confirmed their hypothesis.
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Advantages of CFCs
Unreactive. Non-flammable. Harmless.
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Advantages + Disadvantages of replacement compounds for CFCs
HCFCs-broken down in atmosphere in 10-20 yrs, smaller effect GHG!!! HFCs-don't contain chlorine, GHG!!
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UV radiation breaks Carbon-Halogen Bonds
Carbon-Halogen bond splits homolytically=2 free radicals. Carbon-iodine bond most likely to break, carbon-fluorine bond least likely, as has the highest bond enthalpy.
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How does ozone act as sunscreen
Ozone layer removes all UVC radiation and about 90% of the UVB. UVB damages the DNA in cells causing skin cancer, + main cause of sunburn.
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Polluting effects of ozone in the troposphere
In heavily industrialised areas, ozone mixes with solid particles of carbon and many other substances causing photochemical smog. Which affects the lungs, and can trigger asthma attacks.
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The suns radiation
Gives out radiation cause of its nuclear processes in its core. Mainly gives out visible and infrared radiation, along with small amounts of UV.
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Molecules change in vibrational energy states
Some molecules absorb energy from IR, this extra energy makes their covalent bonds vibrate. Only molecules of diff atoms abosrb IR as polarities change when they vibrate.
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Frequencies of radiation correspond to particular amounts of energy absorbed
Gas molecules have certain fixed energy levels called quantised levels. A bonds energy can only jump from 1 level to another, so diff molecules absorb diff frequencies of radiation.
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UV and visible radiation give electrons more energy
When UV/visible radiation hit a molecule of gas, the electrons can absorb the energy and jump up to their next energy level, the energy is quantised so only specific frequencies are absorbed, if enough energy's absorbed, bonds break=free radicals.
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Energy from radiation calculation
∆E=hv, Energy=Planck's constant (6.63x10^-34) x frequency
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Greenhouse Effect
Solar energy reaches Earth mainly as visible/UV. Earth absorbs some of this energy, heats up and radiates IR. GHG in troposphere absorb some of this IR in the 'IR window'. Absorption of IR by GHG increase vibrational energy of bonds,
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Greenhouse Effect 1
This energy transferred to other molecules by collisions, thus increasing their kinetic energy and raising the temp. GHG also re-emit some of the absorbed IR in all directions, some heats up the earth. ^ conc of GHG ^greenhouse effect.
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Different approaches to control carbon dioxide emissions
Burn fewer fossil fuels, increase photosynthesis, and bury/react carbon dioxide.
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Hydrogen Bonds form
Only happens when hydrogen covalently bonded to F2, N2, O2, as they're electronegative so draw bonding electrons away from H. Bond is polarised and H has high density charge so weak H bonds with lone pairs form.
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What to look for to see if a H bond is present
-OH or -NH.
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Hydrogen bonds make high boiling points
Lots of energy is needed to overcome intermolecular forces and hydrogen bonds present.
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Hydrogen bonds mean some polymers dissolve in water
If OH present, strong hydrogen bonding so insoluble. Polymers are insoluble when very many/very few internal H bonds, soluble when an intermediate number of H bonds.
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Aldehydes
Carbonyl group at end of Carbon Chain e.g. CH2CH2CHO
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Ketones
Carbonyl group anywhere in the chain e.g. CH3COCH3
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Carboxylic acids
Contain -COOH
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Primary structure of alcohols
The carbon with the -OH attached is attached to one alkyl group e.g. propan-1-ol
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Secondary structure of alcohols
The carbon with the -OH attached is attached to two alkyl groups e.g. propan-2-ol
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Tertiary structure of alcohols
The carbon with the -OH attached is attached to three alkyl groups e.g. 2methylpropan-2-ol
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Heating under reflux for reactions involving volatile liquids
1) Heat ethanol with potassium dichromate(VI) solution + sulfuric acid in test tube, =ethanal. 2) Heat excess alcohol with a controlled amount of oxidising agent so aldehyde distilled off. 3) Mix alcohol with excess oxidising agent under reflux.
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Reflux
Increase the temperature of an organic reaction to boiling without losing volatile solvents, reactants or products.
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Elimination reaction
Small group of atoms break away from larger molecules. 1) Ethanol vapour passed over hot catalyst of pumice stone 2) Or reflux ethanol with excess concentrated sulfuric acid at 170 degrees,
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Addition polymerisation
The double bonds in alkenes can open up and join together to make long chains - polymers.
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Electrophiles
Electron-pair acceptors.
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Addition
Double bonds open up and atoms are added to the carbon atoms
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Carbocation
Positively charged cation
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E/Z isomerism
C=C bonds can't rotate when there are 2 different groups on each carbon. E=opposite sides of bond. Z=same sides of bond. E=Trans, Z=Cis.
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A polymers use depends on its properties
Poly(ethene)=bags, bottles. Poly(propene)=bottle crates, rope. Poly(chloroethene)=water pipes, building material. Poly(tetrafluoroethene)=coating 4 frying pans. Polystyrene=expanded polystyrene, insulator.
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Thermoplastic
No cross-linking between chains. Weak intermolecular forces. Easy to melt and easy to remould.
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Thermoset
Covalent cross-links. 3D giant covalent structure. Too much heat makes it char. Strong, hard, rigid and insoluble.
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Co-polymer
Made from more than one type of polymer in random order.
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Other cards in this set

Card 2

Front

Giant lattice. Covalently bonds with 4 O atoms. tetrahedral shape. Crystal lattice. O atoms only bond with 2 Si atoms. Hard crystalline solid, h.m.p.t. Insoluble in solvent. Doesn't conduct electricity.

Back

Silicon Oxide

Card 3

Front

CO2=small molecules, each C forms double bond with O atoms. Gas @ r.t. as weak i.d-i.d forces. Dissolves in H2O. SiO2=giant lattice. Si atom forms single bonds with 4 O atoms. H.b.p.t. insoluble.

Back

Preview of the back of card 3

Card 4

Front

Concn=Particles closer together, collide more -more chances to react. Pressure=Particles closer together, collide more-more chance of reacting. Surface area=More particles come in contact with other reactants, -speedier reaction.

Back

Preview of the back of card 4

Card 5

Front

Minimum amount of kinetic energy particles need to react

Back

Preview of the back of card 5
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