CHEMISTRY UNIT 2 (post mocks)
- 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)
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
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
Boltzmann distribution
DIAGRAM:
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)
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
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
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)
common polymers
1)
common polymers (2)
4)
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 ...
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
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
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
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
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)
oxidation of alcohols
PRIMARY ALCOHOLS ------> ALDEHYDE ------> CARBOXYLIC ACID
SECONDARY ALCOHOL ------> KEYTONE
TERTIARY ALCOHOL ------> (NO REACTION)
esterification of alcohols
CARBOXYLIC ACID + ALCOHOL --(conc. H2SO4)--> ESTER + WATER
NAMING ESTER
- A lcohol
- B efore
- C arboxylic acid
E.g
% 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
hydrolysis of halogenoalkanes (nucleophilic substi
DIAGRAM
atom economy
molecular mass of desired product
------------------------------------------------ X 100
sum of molecular masses of all products
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
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-
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
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)
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
greenhouse effect
H2O + CO2 + CH4
O - H
C = O
C - H
bond are very good at absorbing radiation (MOVING DIPOLES)
BONDS VIBRATE + ROTATE
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
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
OZONE LAYER (2)
FORMATION
HOW O3 ABSORBS LIGHT
CYCLE BALANCED (EQUILIBRIUM)
OZONE CAN BE REMOVED NATURALLY
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
OZONE depletion (2)
another RADICAL that can DESTROY O3 is NO.
PROPAGATION
1)
2)
OVERALL
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
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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