CHEMISTRY UNIT 2 (post mocks)

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  • Created by: charlie
  • Created on: 04-03-14 20:14

rate of reaction

EQUATION: 

factors:

  • temp (>or equal to Ea)
  • pressure (gases) or concentration (solution)
  • surface area 
  • catalyst/enzyme 
  • light (some)

collision theory 

  • 'molecules must have suffieicent energy to overcome the activation energy (bonds break)'
  • molecules have to be correctly orientated - (ELECTROPHILIC ADDITION)
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catalysts

'speed up reactions without being used'  HOMOGENEOUS 

  • in same phase (e.g aq)
  • ethanol (aq) + ethanoic acid (aq) --H+(aq)--> ethyl ethanoate (aq) + water 

HETEROGENEOUS 

  • different phase (e.g. s or g)
  • N2(g) + 3H2(g) --Fe(s)--> 2NH3 (g) 

ENZYMATIC 

  • biological catalysts 
  • low temp. 30d.c --> 40d.c
  • cheap + specific 
  • biodegradable 
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catalysts (2)

enthalpy change diagram with catalyst: 

USING CATALYSTS:

  • speeds up reaction 
  • lowers Ea
  • reduces energy costs --> less fossi fuels burnt --> save crude oil --> less CO2 / global warming --> improve yield --> less waste 
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Boltzmann distribution

DIAGRAM: 

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equilibrium

'if rate of forward reaction is equal to rate of reverse reaction and system is closed, then reaction has reached equilibrium' 

'a system at equilibrium will have CONSTANT macroscopic properties (visible) but its DYNAMIC at molecular level' 

  • INC TEMP = eqm. moves LEFT (ENDO)
  • DEC TEMP = eqm. moves RIGHT (EXO)
  • INC PRESS = moves to side with FEWER GAS MOLES (dec. press)
  • DEC PRESS = moves to side with MORE GAS MOLES (inc. press)
  • INC CONCEN (reactant) = moves RIGHT gets rid of EXTRA REACTANT (makes more product)
  • INC CONCEN (products) = move LEFT gets rid of EXTRA PRODUCTS (makes more reactants)
  • DEC CONCEN = opposite effect 
  • CATALYST = position is NOT CHANGES (speeds up both sides of reaction) 
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equilibrium (CASE STUDIES)

1.      2NO2(g) <---> N2O4(g)              brown <---> colourless          /\H = -57 KJ/mol 

  • INC TEMP = BROWNER as eqm. shifts LEFT (to absorb heat)
  • INC PRESS = LIGHTER as eqm. shifts RIGHT (less moles)

2.     CaCO3(s) <---> CaO(s)  + CO2(g)          /\H = +ve KJ/mol

  • INC TEMP = more CaO produced as eqm. shifts RIGHT 
  • INC PRESS = less CaO produced as eqm. shifts LEFT 

3.     N2(g) + 3H2(g) <--Fe--> 2NH3(g)         /_\H = -92 KJ/mol

  • INC TEMP = eqm. shifts LEFT (endothermic direction)
  • INC CONCEN (reactants) = eqm. shifts RIGHT (make more products)
  • INC PRESSURE = eqm. shifts RIGHT (less moles of gase)

WANT EQM. ON RIGHTS AS IT INC. PRODUCTS 

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industrial importance of alkenes

MANUFACTURE OF MARGARINE 

HYDROGENATION (hardens oils that are polyunsaturated --> can spread on brad + not soak in)

  • adds H molecule across double bond in ADDITION REACTION 
  • alters individual molecule in oil so SOLIDIFIES 
  • add H molecule across DIFF. NUMBER of double bonds = margarine of diff. hardness 
  • PARTIAL HYDROGENATION -> CIS double bonds to TRANS as a by-products (bad for health)

ADDITION POLYMERISATION (many monomers added to make polymer)

  • monomer units based on diff. alkenes 
  • monomers UNSATURATED 
  • forms SATURATED CHAIN
  • made from 1 monomer only 

e.g. DIAGRAM 

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processes of addition polymerisation

RADICAL POLYMERISATION 

  • 200d.c 
  • very HIGH pressure 
  • BRANCHING of polymer chain + production of polymer mixtures 
  • e.g. poly(phenylethene) poly(styrene) branched poly(ethene)

ZIEGLER-NATTA PROCESS

  • 60d.c
  • specialist catalyst - (TiCl3  'or'  Al(C2H5)Cl)
  • low conversion = recycled 
  • most common method to produce UNBRANCHED 
  • e.g. poly(ethene)
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common polymers

1)

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common polymers (2)

4)

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polymer uses

  • do not react with chemicals inside them 
  • fairly durable 
  • dont break down naturally 

POLYSTYRENE 

  • foam packaging, insulating, model making, food retail 
  • replaced by BIODEGRADEABLE MATERIALS 

POLYPROYLENE 

  • food packaging, synthetic ropes, lab equipment (chemically resistant) 

POLYTHENE 

  • grocery bags, shampoo, toys ... 
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waste management - recycling

2 stages  SORTING 

  • identification codes 
  • machines using optical scanning 
  • PVC releases poisonous dioxins when released 

RECLAIMATION

  • process polymers 
  • mechanically chopped
  • washed to remove impurities 
  • PET = carpets, clothing, bottles 
  • HDPE = hard plastics 
  • LDPE = plastic refuse sacs 
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polymers - fuel source + PVC

ELECTRICITY 

  • POLYMER + HEAT ---> electrical energy (heat)

FEED STROCK RECYCLING 

  • POLYMER ---> SYNTHESIS GAS (H2+CO2)
  • used as chemical feedstock for conversion into useful products or fuel at oil refineries

RECYCLIN PVC 

  • high Cl content --> uneconomical (end product is more expenisive than made from crue oil)

INCINERATION =          release toxic fumes + corrosion in plant itself ---> (acidic HCL) ---> has POLLUTION CONTROL APPARATUS 

COMMERCIAL PVC RECYCLING PLANT =          separated from other scrap by dissolving in solvent --> high quality recovered as precip. ---> used again e.g coating wires 

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bioplastics

  • made from raw materials: STARCH, MAIZE, CELLULOSE, LACTIC ACID 
  • manufactured by non hazardous process 
  • degrade naturally ---> CO2 + H2O

BIODEGRADABLE 

  • break down as a result of bacterial activity 
  • poly(lactic acid) in cold drink cups biodegrades in 180 days 

COMPOSTABLE 

  • break down by biolytic process during composting --> CO2 + H2O + inorganic compounds + biomass
  • less resistance to break down than polystyrene 
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alcohol (ethanol) production

FERMENTAION OF SUGAR (sugar / starch)

  • ethanol 14% alc. vol. + inc. toxicity ceases enzyme function 
  • low temp (25d.c --> 37d.c) CHEAP 
  • yeast catalyst = enzyme zymase 
  • anaerobic or when oxidised produces ETHANAL or ETHANOIC ACID (different flvour)

C6H12O6(aq) --yeast--> 2CH3CH2OH(aq) + 2CO2(g)

HYDRATION OF ETHENE 

  • catalyst = phosphoric acid, H3PO4
  • high temp (300d.c) + moderate pressure (60 atm) EXPENSIVE 
  • continuous 
  • H2C=CH2(g) + H20(g) <--H3PO4--> CH3CHOH(l)
  • 5% complete conversion ---> recycled --> 95% conversion 
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classification of alcohols

"depends on number of alkyl groups attached to the carbon carrying the alcohol group, C-OH"

PRIMARY

  • -OH group attached to carbon with no alkyl groups / or bonded to 1 alkyl group 
  • DIAGRAM (butan-1-ol)

SECONDARY 

  • -OH group attached to a carbon atoms bonded to 2 alkyl groups 
  • DIAGRAM (propan-2-ol)

TERTIARY 

  • -OH group attached to a carbon atom bonded to 3 alkyl groups 
  • DIAGRAM (2-methyl-2-ol)
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oxidation of alcohols

PRIMARY ALCOHOLS                      ------>       ALDEHYDE         ------>          CARBOXYLIC ACID 

SECONDARY ALCOHOL                 ------>             KEYTONE 

TERTIARY ALCOHOL                      ------> (NO REACTION) 

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esterification of alcohols

CARBOXYLIC ACID + ALCOHOL --(conc. H2SO4)--> ESTER + WATER 

NAMING ESTER 

  • A lcohol 
  • B efore 
  • C arboxylic acid 

E.g 

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% yield

PRACTICAL AMOUNT, in mol, of product 

----------------------------------------------------       X 100

THEORETICAL AMOUNT, in mol, of product 

E.g

1) work out moles of wanted product 

2) work out moles of limiting reactant 

3) divide moles of "wanted product" by "limiting reactant"

4) x by 100 

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hydrolysis of halogenoalkanes (nucleophilic substi

DIAGRAM 

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atom economy

molecular mass of desired product 

------------------------------------------------   X 100 

sum of molecular masses of all products 

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mass spectrometry

uses:

  • identify unknown compounds / determine abundance of each isotope in element 
  • gain understanding of chemical structure + properties of element 

medical + industrial uses :

  • monitor patients breathing through surgery / detecting banned drugs 
  • analyse molecules in space / detect toxic chemicals in marine life 

how it works 

  • determines mass of molecule/isotope by measuring mass-to-charge ratio of ions 

CALCULATING RAM FROM MASS SPECTRA  ...

diagram 

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mass spectrometry in organic compounds

how it works 

  • placed in mass spectrometer + some molecules lose electrons + ionised 
  • resultants ion is MOLECULAR ION given symbol M+

e.g. 

C2H5OH   +   e-  =>   C2H5OH+   +   2e- 

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fragmentation

  • excess energy from ionisation process transferred to molecular ions making it vibrate 
  • bonds wekan + MOLECULAR ION SPLITS 
  • forms FRAGMENT ION

e.g. 

C2H5OH+    =>     CH3    +   CH2OH+ (Fragment ion)

FRAMENTATION PATTERNS 

  • highest peak on the right shows MOLECULAR ION (has highest Mr value)
  • molecule then breaks up and gets smaller as moves left (shown by peaks)
  • E.g 
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IR spectroscopy

  • when bonds abosrb IR  they:  BEND + STRETCH 

bond vibrations have own frequency depening on... 

  • bond strength 
  • bond length 
  • mass of each atom in a bond 

how it works 

  • beam with all frequencies passed through sample 
  • molecule absorbs some frequencies 

uses 

  • quality control in perfume manufacture 
  • drug analysis 

(INFORMATION ON BACK OF DATA SHEET)

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CO2 uses

BY-PRODUCT OF FERMENTATION 

FOAM - replaced CFC's as blowing agents 

SOLVENT 

  • many are flammable, volatile + toxic 
  • alter temp + pressure for CO2 --> supercritical CO2 (scCO2)

DECAFFEINATED COFFEE - CO2 addded so only caffeine removed 

BEER - natural fizz

DRY CLEANING - non-toxic, scCO2 + water 

TOXIC WASTE - organic compounds dissolve in scCO2 

CHEMICAL SYNTHESIS -scCO2 as solvent / reactant ---> control properties for high % yield 

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greenhouse effect

H2O + CO2 + CH4 

O - H 

C = O

C - H

bond are very good at absorbing radiation (MOVING DIPOLES)

BONDS VIBRATE + ROTATE

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solutions to greenhouse effect

  • inc. renewable + nuclear energy 
  • inc. energy efficiency measures 

CARBON CAPTURE + STORAGE (CCS)

  • "carbon can be captured by DECARBONISING FUEL in process known as REFORMING"
  • CH4(g) + 2H2O(g) => CO2(g) + 4H2(g)
  • H2(g) burnt cleanly to produce water 
  • CO2(g) stored in porous rocks (e.g. emptied oil wells) 
  • injecting CO2(g) into oil wells means more oil recovered 

STORED AS CARBONATES - occurs naturally --> MINERAL STORAGE 

  • CaO(s) + CO2(g) => CaC03(s) (stable carbonate rock)
  • HOWEVER CaO produced in lime kilns requiring lots of ENERGY 
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OZONE LAYER

DIAGRAM 

low level ozone produced in photochemical smog causes repiratory problems:

  • GOOD: stratosphere filters UV light that would otherwise cause cell damage / cancer 
  • BAD: troposhere causes SMOG 
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OZONE LAYER (2)

FORMATION 

HOW O3 ABSORBS LIGHT 

CYCLE BALANCED (EQUILIBRIUM)

OZONE CAN BE REMOVED NATURALLY 

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OZONE depletion

CFC's  e.g. CF2Cl2 (very unreactive)

USES  - fridges (coolants) / aerosols / fire extinguishers 

DAMAGE - diffuse up into stratosphere where UV light can create Cl. 

INITIATION 

PROPAGATION 

1)

2)

OVERALL 


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OZONE depletion (2)

another RADICAL that can  DESTROY O3 is NO.

PROPAGATION

1)

2)

OVERALL 

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controlling air pollutants from cars

CO 

  • toxic / poisonous 
  • higher affinity for Hb than CO2 
  • drowsiness / headache / death 

NO / NO2 

  • acidic --> acid rain 
  • O3 respiratory irritant 
  • photochemical smog --> eye irritant 

CxHy (unburnt HC's)

  • includes C6H6 (benzene) --> carginogenic 
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catalytic converter (rode to the palladium wearing

  • Rhodium, Rh 
  • Palladium, Pd
  • Platinum, Pt 

METALS CATALYSE REMOVAL OF POLLUTANT GASES: 

CO + 1/2 O2 => CO2 

C6H6 + 9/2 O2 => 6CO2 + 3H2O 

CO + 2NO => N2 + CO2 

on the surface: 

  • 1) gases ADsorbed 
  • 2) bonds weaken + break
  • 3) new bonds form 
  • 4) products DEsorbed 
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