Chemistry Edexcel Unit 4.pptx

UV to initiate reactions
• NAME: Ultraviolet (UV) radiation
• TYPE: Form of electromagnetic radiation
• WAVELENGTH: Wavelength between that of
visible light and x-rays  400nm to 10nm
• USE: Enough energy to split molecules 
produce free radicals
• MECHANISM: Homolytic fission  each atom
takes one electron from covalent bond
• EXAMPLE: E.g. splitting of chlorine molecule into
2 chlorine free radicals

Chlorine and methane reaction using
UV radiation
• Initiation step  free radicals created
• Cl2 (+ UV)  Cl. + Cl.
• Propagation steps  free radicals re-created
• CH4 + Cl.  CH3
. + HCl
• CH3
. + Cl2  CH3Cl + Cl.
• Termination steps  two free radicals combine
• Cl. + Cl.  Cl2
• Cl. + CH3
.  CH3Cl
• CH3
. + CH3
.  C2H6

Creation of chlorine free radicals from
CFC’s using UV radiation
• WHERE: In outer edge of atmosphere
• TYPE OF UV: UV from sunlight
• INITIATION STEP: CF3Cl (+ UV)  CF3 + Cl.
• DANGER: Ozone broken down by Cl. 
needed to protect Earth’s surface from UV
radiation
• PROPAGATION STEPS: Cl. + O3  O2 + ClO.ClO.
+ O3  Cl. + 2O2

Microwaves
• TYPE: Form of electromagnetic radiation
• WAVELENGTH: Wavelength between that of infrared and radio
waves  1mm to 1m
• USE: For heating/communications
• WAVELENGTH OF MICOWAVES FOR HEATING: Microwave oven
uses wavelength of 12.24cm
• POLAR BONDS: Polar bond when there are 2 atoms of different
electronegativity's in a covalent bond, causing electrons to be
pulled towards the more electronegative atom
• WATER POLARITY: Oxygen of water more electronegative than
hydrogen so electrons pulled towards oxygen atom  polar bonds
• HOW MICROWAVE OVENS WORK: Microwaves pass through food,
causing electromagnetic field; polar molecules try to line up with
electromagnetic field by rotating; polar molecules collide, releasing
heat energy

Mass spectrometry
• USE: To find relative molecular mass (Mr)
• IONISATION: Electrons bombard sample molecules,
removing electrons to form ions
• M PEAK: Molecular ion peak is second from last peak
on spectrum
• Mr: Molecular mass of ions = mass/charge of the M
peak
• BASE PEAK: Base peak is the highest peak
• RELATIVE ABUNDANCE: Relative abundance for base
peak set at 100%  all other peaks measured as a
percentage of this

Molecular ion
• FRAGMENTS: Fragmentation pattern caused
by fragments made by bombardment of
sample with electrons
• FREE RADICALS: Only ions show up on the
mass spectrum  free radicals are lost

Identification of a molecule using mass
spectrometry
• Mr: Mr = mass/charge of M peak
• STRUCTURAL FORMULA: Fragmentation
pattern used to find structural formula e.g.
determining functional group
• CHECKING: Draw out structural formula found
from fragmentation pattern and work out its
Mr  should equal the Mr found using M
peak

Common
fragments
Fragment Mr
CH3 15
C2H5 29
C3H7 43
OH 17
CHO 29
COOH 45

NMR determining molecular structure
• NAME: Nuclear magnetic resonance (NMR)
spectroscopy
• WHAT: Examines how magnetic fields react when you
put it in a larger, external magnetic field by measuring
absorption of energy
• NUCLEAR SPIN: Any atomic nucleus with odd numbers
of nucleons (protons and neutrons) has nuclear spin
which gives it a weak magnetic field
• PROTON NMR: Hydrogen nuclei are single protons, so
proton NMR can be used to find how many hydrogen
atoms there are in an organic molecule and how
they’re arranged

Alignment of protons in an external
magnetic field
• NORMAL PROTON SPIN: Protons normally spin in random
directions so their magnetic fields cancel out
• SPIN WITH STRONG EXTERNAL MAGNETIC FIELD: When a
strong external magnetic field is applied, protons align
themselves either with or against the magnetic field
(aligned or opposing)
• ENERGY OF PROTONS: Aligned protons are at a lower
energy than opposing protons
• RADIO WAVES: When protons absorb radio waves they can
flip to become opposing; opposing protons can emit
electrons to become aligned
• OVERALL EFFECT: More aligned protons, so an overall
absorption of energy

Absorptions in different environments
• SHIELDING: Surrounding electrons and other
atoms/groups of atoms shield protons from
the effect of external magnetic fields
• ENVIRONMENT: To be in the same
environment, atoms must be joined to exactly
the same thing

Chemical shift
• PEAKS OF NMR: Peaks of NMR spectrum show
frequencies at which protons absorb energy
• TMS: Differences in absorption measured against
standard substance such as tetramethylsilane  12
protons in identical environments so has a single peak
away from most peaks of protons of other molecules
• CHEMICAL SHIFT: Chemical shift is the difference in
absorption of a proton relative to TMS
• CALBIRATION: TMS is given a chemical shift of 0 and
TMS is added to the sample for calibration purposes

NMR
• NUMBER OF PROTONS: Area under peak tells you how
many protons in that environment
• MULTIPLETS: Spin-spin coupling  multiplets are
multiple peaks that show the number of hydrogen
atoms on the adjacent carbon
• 1 PROTON ON ADJACENT CARBON: Doublet is a peak
split into 2 and shows one proton on adjacent carbons
• 2 PROTONS ON ADJACENT CARBON: Triplet is a peak
split into 3 and shows two protons on adjacent carbons
• 3 PROTONS ON ADJACENT CARBONS: Quartet is a
peak split into 4 and shows three protons on adjacent
carbons

Magnetic resonance
• MRI: Magnetic resonance imaging scanners study
internal structures in the body  works the same as
NMR spectroscopy
• HOW: Body is irradiated with radio waves, hydrogen
nuclei in water molecules interact with radio waves
and different frequencies absorbed depending on the
type of tissue the water molecules are in
• BUILDING 3D IMAGE: 3D image built by using a
computer to combine series of photos taken when
beam of radio waves is moved down the body
• USE: For cancer treatment, bone/joint treatment and
studies of the brain and cardiovascular system

Other uses of NMR
• PHARMACEUTICAL: Monitor composition of
products to make sure they are pure, so drug
is not contaminated

Infrared spectroscopy to identify
organic molecules
• HOW: Beam of IR radiation goes through
sample, energy is absorbed by bonds in
molecules, increasing their vibrational energy
• BONDS: Different bonds absorb different
wavelengths
• POSITION OF BONDS: Bonds in different
places within a molecule absorb different
wavelengths

IR spectrum of different functional
groups
Functional
group
Where it’s found Frequency/wavelength
Type of
absorption
C-H Most organic molecules 2800-3100 Strong, sharp
O-H Alcohols 3200-3500 Strong, broad
O-H Carboxylic acids 2500-3300 Medium, broad
N-H Amines 3200-3500 Strong, sharp
C=O Carbonyls, carboxylic acids 1680-1750 Strong, sharp
C-O Esters, carboxylic acids 1100-1310 Strong, sharp
C-X Halogenoalkanes 500-1000 Strong, sharp

Uses of IR spectroscopy
• CHEMICAL INDUSTRY: Measuring the point
where one functional group changes to another
• POLYMER MANUFACTURE: Degree of
polymerisation measured by recording
absorption at frequency of the double bond in
the monomer
• OXIDATION OF POLYMERS: Absorption at 1700 is
shown when the polymer has been oxidised

Separation and identification
• MOBILE PHASE: A liquid or gas in which
molecules can move
• STATIONARY PHASE: A solid, or a liquid held in
a solid, in which the molecules can‘t move
• HOW: Components of mix separate when
mobile phase moves through a stationary
phase
• GC: Gas chromatography
• HPLC: High pressure liquid chromatography

Gas chromatography
• STATIONARY PHASE: Viscous liquid such as oil coating the inside of
a coiled tube
• MOBILE PHASE: Unreactive carrier gas e.g. nitrogen
• HOW: Sample injected into heated carrier gas stream as a gas or
liquid, each component absorbs to the stationary phase in different
amounts, the more absorption the longer it takes to pass through
the tube
• RETENTION TIME: The amount of time the mobile phase spends
absorbed in the stationary phase
• DETECTOR: Uses thermal conductivity of gases to draw
chromatogram
• PEAK OF CHROMATOGRAM: Retention time
• AREA UNDER CHROMATOGRAM: Relative amount of each
compound

High pressure liquid chromatography
• STATIONARY PHASE: Small particles of solid packed in
a tube e.g. silica bonded to hydrocarbons
• MOBILE PHASE: Polar mixture e.g. methanol and water
• HOW: Sample injected into high pressure stream of
mobile phase, carried through tube as a solution and
analysed by a mass spectrometer
• DETECTOR: Absorption of UV light passed through
sample
• USE: When sample is heat-sensitive, has a high boiling
point

Chromatography to check purity of
sample
• GC: Used in chemical industry to check purity
of products in continuous production by
diverting product to GC at regular time
intervals
• HPLC: Used to check cleanliness of equipment
used in drug manufacture as it is a very
sensitive analysis, so even small levels of
impurities and residues are detected

Carbonyl group
• CARBONYL GROUP: C=O
• ALDEHYDE FUNCTIONAL GROUP: RCH=O
• ALDEHYDE SUFFIX: -al
• KETONE FUNCTIONAL GROUP: RCR’=O
• KETONE SUFFIX: -one

Hydrogen bonds
• INTERMOLECULAR: No intermolecular H-bonds as there is
no H-O, H-F or H-N bond
• BOILING POINTS: Lower than equivalent alcohols but
higher than equivalent alkanes
• H-BOND WITH WATER: Polar C=O bond of carbonyls
creates slightly negative O, which forms H-bonds with
slightly positive H atom of water
• DISSOLVING IN WATER: Small carbonyls dissolve because
they form hydrogen bonds, which make up for the breaking
of intermolecular forces; larger carbonyls don’t dissolve
because the energy required to break intermolecular forces
is not compensated for by the formation of H-bonds with
water

HCN nucleophilic addition
• NUCLEOPHILE: An electron rich atom that donates
electrons to an electron deficient molecule
• REACTANTS: Carbonyl, potassium cyanide, hydrogen
cyanide
• PRODUCTS: Cyanide ions (catalyst), hydroxynitrile
• 1ST STEP: CN- ion attacks C-atom, and donates a pair of
electrons; electrons from double bond transfer to the
oxygen to make O-
• 2ND STEP: H+ from HCN bonds to O-, to form hydroxynitrile
• SAFETY: HCN is a highly toxic gas so use fume cupboard
• OPTICAL ACTIVITY: Carbonyl group is planar, so if reactant
is chiral, the product will be a racemic mixture

Test for carbonyl group
• REAGENT: Brady’s reagent/2,4-
dinitrophenylhydrazine
• CONDITIONS: Dissolved in methanol and conc
sulfuric acid
• POSITIVE RESULT: Bright orange precipitate
• IDENTIFYING THE CARBONYL: precipitate
recrystallized, melting point measured and
compared to table of known melting points

Oxidation of aldehydes to carboxylic
acids
• REAGENT: Potassium dichromate (6)
• CONDITIONS: Heated under reflux with dil
sulfuric acid
• POSITIVE RESULT: Orange  green
• EQUATION: RCH=O + [O]  RC=OOH

Reduction of carbonyls
• ALDEHYDES: Form primary alcohols when
reduced
• EQUATION: RCH=O + 2[H]  RCH2OH
• KETONES: Form secondary alcohols when
reduced
• EQUATION: RCR’=O + 2[H]  RCHR’OH
• REAGENT: LiALH4 (lithium aluminium hydride)
• CONDITIONS: In dry ether

Test for methyl carbonyl group
• REAGENT: Iodine
• CONDITIONS: Heated in the presence of alkali
• POSITIVE RESULT: Yellow precipitate of
triiodomethane (CHI3), smell of antiseptic

Carboxyls
• CARBOXYL GROUP: -COOH
• FUNCTIONAL GROUP OF CARBOXYLIC ACIDS:
RCOOH
• CARBOXYLIC ACID SUFFIX: -oic acid
• pH: Weak acids; partially dissociate to
carboxylate ions and H+ ions in water

Solubility of carboxylic acids
• POLARITY: Carboxylic acids are polar because electrons
are pulled towards the more electronegative O-atoms
• BOILING POINTS: High because the molecules are
polar
• SOLUBILITY: Very soluble in water because they can
form hydrogen bonds with water molecules; solubility
decreases as C-chain length increases because London
forces increase as the number of electrons increase
• DIMERS: Formed when a liquid carboxylic acid
hydrogen bonds to just one other carboxylic acid
molecule; increases size so increases intermolecular
forces and boiling point

Formation of carboxylic acids
OXIDATION OF PRIMARY
ALCOHOLS AND ALDEHYDES
• OVERVIEW: Primary alcohol
 Aldehyde  Carboxylic
acid
• EQUATION: RCH2OH + [O]
 RCH=O + [O]  RC=OOH
HYDROLYSIS OF NITRILES
• CONDITIONS: Heat under
reflux with dilute
hydrochloric acid, distil off
carboxylic acid
• EQUATION: CH3CN + 2H2O +
HCl  CH3C=OOH

Formation of salts
• REACTANTS: Aqueous
alkali, carboxylic acid
• PRODUCTS: Salt (-oate),
water
• TYPE OF REACTION:
Neutralisation
• REACTANTS: Carbonate
(CO3
2-) or hydrogen
carbonate (HCO3
-),
carboxylic acid
• PRODUCT: Salt, carbon
dioxide and water
• TYPE OF REACTION:
Neutralisation

Reactions
• TYPE: Reduction
• REAGENT: LiAlH4
• CONDITIONS: Dry ether
• PRODUCT: Primary
alcohol
• REAGENT: PCl5
[phosphorus (5)
chloride]
• PRODUCT: Acyl chloride,
POCl3, HCl

Titrations
• INDICATOR: Phenolphthalein
• STANDARD SOLUTION: Sodium hydroxide
• END POINT: Pink
• CALCULATING MOLS: Mols = (vol x
conc)/1000

Formation of esters
• REACTANTS: Carboxylic acid, alcohol, acid
catalyst
• PRODUCTS: Ester, water
• DISTILATION: Reversible reaction so product
distilled off as it is formed
• REMOVING ACID: Product mixed with sodium
carbonate to remove unreacted acid

Esters
• ALKYL GROUP: Comes from alcohol
• CARBOXYL GROUP: Comes from carboxylic
acid; given suffix –oate
• EXAMPLE: Methanal + Enthanoic acid 
Methyl Ethanoate + Water

Hydrolysis of esters
• TYPE: Acid hydrolysis
• REACTANTS: Ester,
water
• PRODUCTS: Carboxylic
acid, alcohol
• CONDITIONS: Heat
under reflux with dil
HCl/sulfuric acid; lots of
water to push
equilibrium right
• TYPE: Base hydrolysis
• REACTANTS: Ester,
dilute alkali
• PRODUCTS: Salt,
alcohol
• CONDITIONS: Heat
under reflux

Making soaps
• TYPE: Base hydrolysis
• ALCOHOL: Glycerol
• CARBOXYLIC ACID: Fatty acids
• HOW: Heat fats with sodium hydroxide, to
form glycerol and sodium salts (soap), then
add sodium chloride so soap crusts on surface
of the liquid

Transesterification
• WHAT: Swapping the alcohol part of the ester
with another alcohol
• LOW FAT SPREADS: Hydrogenation used to be the
method for producing spreads, but that produces
trans-fats so now transesterification is used to
create spreads from oils
• BIODIESEL: Renewable fuel made from vegetable
oils/animal fats by transesterification of ester
with methanol/ethanol to produce methyl/ethyl
esters

Formation of polyesters
• REACTANTS: Dicarboxyl, diol
• PRODUCTS: Polyester, water
• ESTER LINKS: C-O-C

Acyl chlorides
• FUNCTIONAL GROUP: COCl
• SUFFIX: -oyl chloride

Reactions
• WITH WATER: Acyl chloride + water  carboxylic
acid + hydrochloric acid
• WITH ALCOHOLS (REFLUX): Acyl chloride +
alcohol  ester + hydrochloric acid
• WITH AMMONIA: Acyl chloride + ammonia 
amide + hydrochloric acid
• WITH AMINES: Acyl chloride + amine  N-
substituted amide + hydrochloric acid
• HCl: Released as gas so steamy fumes are
observed

Structural isomers
• DEFINITION: Same molecular formula,
different structural formula
• C-CHAIN ISOMERISM: Different lengths of
longest carbon chain due to branching
• POSITIONAL ISOMERISM: Same functional
group, joined to different C-atom
• FUNCTIONAL GROUP ISOMERISM: Different
functional group

Stereoisomers
• DEFINITION: Same molecular and structural formula
but different 3D arrangement of atoms
• E/Z ISOMERISM: Priority groups attached to carbons of
C=C on either same side (Z) or opposite side (E); no
rotation around pi-bond at room temperature
• OPTICAL ISOMERISM: Chiral carbon (carbon with four
different groups attached) produces enantiomers,
which rotate the plane of plane-polarised light in
opposite directions
• RACEMIC MIX: Equimolar quantities of each
enantiomer of a chiral compound, so mixture is not
optically active

Nucleophilic substitution mechanisms
and optical activity
• SN1: Start with a single, chiral product;
intermediate is planar so nucleophile can
attack from either side; produces both
enantiomers, racemic mix
• SN2: Start with a single, chiral product;
nucleophile attacks from opposite side;
product has opposite optical activity to
reactant

Acids and bases
• ACID: Proton-donors by releasing H+ ions when in
aqueous solution
• HYDROXONIUM IONS: H+ ions released combine
with water to form H3O+ ions
• BASE: Proton-acceptors by combining with H+
ions of water
• STRONG ACIDS: Fully dissociate to H+ and A- ions
in aqueous solution
• WEAK ACIDS: Only slightly dissociate to H+ and A-
ions in aqueous solution

Conjugate pairs
• CONJUGATE ACID: Base + H+
• CONJUGATE BASE: Acid – H+
• CONJUGATE PAIR: Acid and conjugate
base/Base and conjugate acid

Water
• AS ACID: Donates a proton to form hydroxide
ions
• AS BASE: Accepts a proton to form hydroxonium
ions
• DISSOCIATION: Very little dissociation;
equilibrium lies on left
• IONIC PRODUCT OF WATER: Kw = [H+][OH-]
• VALUE OF Kw: At 298K = 1.0x10-14 mol2dm-6
• pKw = -logKw
• VALUE OF pKw: At 298K = 14

Acidity of solutions
• NEUTRAL: [H+] = [OH-]
• ACIDIC: [H+] > [OH-]
• ALKALINE: [H+] < [OH-]

pH
• pH = -log[H+]
• STRONG ACIDS: [H+] = [HA]
• pOH = 14 – pH
• Ka = [H+][A-] / [HA]
• WEAK ACID: [H+]2 = Ka[HA]
• ASSUMPTIONS FOR CALCULATING pH OF WEAK
ACID: [HA]initial = [HA]equilibrium; all H+ ions
come from acid (none from water)
• pKa = -logKa
• Ka = 10-pKa

DILUTIONS
• STRONG ACID: 10x dilution increases pH by 1
unit
• WEAK ACID: 10x dilution increases pH by 0.5

TITRATION CURVES AND
INDICATORS

pH curves
• WHAT: Graph of pH plotted against volume of alkali
added
• EQUIVALENCE POINT: All acid is neutralised, resulting
in large change in pH when alkali is added
• RULE OF 2: Strong acid = pH 1, weak acid = pH 3, strong
alkali = pH 13, weak alkali = pH 11
• POSITION OF EQUIVALENCE POINT: Start from pH 7,
go up 3 for strong alkali, down 3 for strong acid
• BUFFER RANGE: When halfway towards equivalence
point for weak acid, strong alkali titration

Indicators
• METHYL ORANGE: Use when there is a strong
acid
• PHENOLPHTHALEIN: Use when there is a
strong alkali
• NO INDICATOR AVAILABLE: When both the
acid and alkali are weak, as there is no sharp
change in pH
• USE EITHER: When strong acid and strong
alkali, as there is a long, sharp change in pH

Titration curves to find pKa of a weak
acid
• HALF-EQUIVALENCE POINT: pH = pKa
• Ka = 10-pKa
• [HA]2 = 10-pKa[HA]

Buffers
• DEFINITION: Resist changes in pH when small amounts of
acid/alkali are added
• ACIDIC BUFFERS: Made from weak acid and salt; pH of less
than 7
• ALKALINE BUFFERS: Made from weak base and salt
• ADDITION OF ACID: H+ conc increases; equilibrium shifts
left to use up excess H+ by it reacting with the base so pH
stays roughly the same
• ADDITION OF BASE: OH- conc increases; equilibrium shifts
to the right to use up excess OH- by reacting with the acid
so pH stays roughly the same
• TITRATION CURVES: Show buffer action for weak acids and
strong bases at half equivalence point

Biological reactions
• ENZYMES: Need a particular pH for them to
act as catalysts otherwise they are denatured
• FOOD PRODUCTS: To prevent changes in pH
caused by bacteria and fungi which lead to the
food deteriorating

Calculating pH
• Ka = [H+][OH-] / [HA]
• [H+] = Ka ([HA]/[OH-])
• pH = -log[H+]
• ASSUMPTIONS: [HA]initial = [HA]equilibrium;
[salt] = [OH-]

EQUILIBRIUM
• REVERSIBLE REACTION: Reaction goes both
ways; both the forward and backward
reactions occur
• DYNAMIC EQUILIBRIUM: No change in
concentration of the reactants and products
as both the forward and backward reactions
occur at equal rates
• CONDITIONS FOR DYNAMIC EQUILIBRIUM TO
OCCUR: Closed system, constant temperature

Reversible industrial reactions
• HABER PROCESS: Manufacture of ammonia
for use in fertilisers and other N-compounds
• REVERSIBLE STAGE OF HABER PROCESS: N2 +
3H2  2NH3
• CONTACT PROCESS: Manufacture of sulfuric
acid for use in fertilisers, dyes, medicines and
batteries
• REVERSIBLE STAGE IN CONTACT PROCESS:
2SO2 + O2  2SO3

Kc
• Kc = [products]no. of mols / [reactants]no. of mols
• TYPE OF EQUILIBRIUM: Only applies for
homogeneous equilibrium
• HETEROGENEOUS EQUILIBRIUM: If
heterogeneous mix of solids and gases or
solids and liquids then leave out the conc of
the solid
• WARNING: Do not use for mix of gases and
liquids

Finding equilibrium concs
• INITIAL MOLS: Use values given or take initial mols to
be 1 for reactants
• CHANGE IN MOLS: Work out using level of dissociation
or no. of mols of product formed (whichever is given)
 remember to include sign (+ if added, - if lost)
• MOLS AT EQUILIBRIUM: Work out by adding change in
mols to initial mols
• CONC AT EQUILIBRIUM: Divide mols at equilibrium by
volume in dm3 (if volume is given in cm3 then divide by
1000 to get it in dm3)  these can be put into Kc
equation

Finding concs in equilibrium mixture
using Kc
• SUBSTITUTION: Substitute in all known values
into the Kc equation
• REARRANGE: Rearrange equation so the
subject is the thing(s) you want to find the
concentration of
• STOCHIOMETRY: Use the number of mols of
substances to calculate the concentration of
each thing

Partial pressures
• TOTAL PRESSURE: Sum of all partial pressures
(p) of individual gases (both reactants and
products)
• p = mole fraction / total pressure
• MOLE FRACTION = number of mols of
particular gas / total number of mols of gas

Kp
• Kp = p(products)no. of mols / p(reactants)no. of mols
• WARNING: Do not use square brackets; these are
not concentrations
• ANOTHER WARNING: For heterogeneous
equilibria, only include gases NOT liquids or gases
• TO CALCULATE: Same process as calculating Kc,
except instead of finding concs at equilibrium,
find partial pressures at equilibrium

Total entropy and equilibrium constant
• TOTAL ENTROPY = RlnK
• R: Gas constant, 8.31JK-1mol-1
• K: Use either Kc or Kp
• RELATIONSHIP: K increases as total entropy
increases

Size of K and reaction progression
• HIGH K (K>1): Greater concentration of product,
equilibrium lies to the right
• LOW K (K<1): Greater concentration of reactants,
equilibrium lies to the left
• DYNAMIC EQUILIBRIUM: Concentrations of reactants
and products does not change when forward and
backward reactions occur at equal rates; K=0
• COMPLETION: If K > 1010 then reaction goes to
completion
• REACTION DOESN’T OCCUR: If K < 10-10
• REVERSIBLE REACTION: If K is between 10-10 and 1010

Effect of temperature of total entropy
• TOTAL ENTROPY = entropy of system +
entropy of surroundings
• ENTROPY OF SURROUNDINGS = - enthalpy
change/temp
• INCREASE TEMP: Magnitude of entropy of
surroundings decreases; if endothermic this
causes total entropy to increase, if exothermic
this causes total entropy to decrease
• DECREASE TEMP: Opposite of increase temp

Principle
• PRINCIPLE: When there’s a change in
pressure/temp, the equilibrium will shift to
counteract the change

Temperatures effect on Kc and Kp
• PRESSURE: Does not effect Kc or Kp
• CATALYSTS: Do not effect Kc or Kp
• TEMPERATURE: Equilibrium shifts to the
endothermic direction when heat is added;
shifts to the exothermic direction when heat is
lost  if equilibrium shifts left then K
decreases, if equilibrium shifts right then K
increases

Temperature and pressures effect on
rate of reaction
• INCREASE TEMP: Increases rate because larger
fraction of molecules have above the
activation energy (major effect) and increase
in energy means particles move faster so
collide more (minor effect)
• INCREASE PRESSSURE: Only has an effect is
reactants are gaseous; increase of pressure
pushes particles closer together so there are
more collisions and the rate increases

Haber process
• EXOTHERMIC: Temperature used (450 degrees) is
a compromise between rate of reaction, which is
increased by increasing temperature, and high
yield, which is decreased by increasing
temperature
• PRESSURE: High pressure gives high yield and
increases rate but is expensive (200 atm used)
• DYNAMIC EQUILIBRIUM: Reaction never reaches
dynamic equilibrium because reaction does not
take place in a closed system  keeps forward
reaction occurring at a fast rate

Maximising atom economy
• % ATOM ECONOMY = mass of atoms in product /
mass of atoms in reactants (X 100)
• RECYCLING: Increases atom economy by reusing
unreacted gases  reactants recycled in Haber
process as equilibrium means that not all
reactants are used up the first time
• FINDING A DIFFERENT ROUTE OF SYNTHESIS:
Synthesis of Ibuprofen was reduced from 4 stages
to 3 stages, increasing atom economy from 40%
to 77%

Control of industrial processes
• TOTAL ENTROPY: Must be positive under the
conditions used for the reaction to occur
• SPEED OF REACTION: Slow rate is not
economical; changes to temp, pressure or
addition of catalyst used to speed up reaction
• ATOM ECONOMY: Kept as high as possible e.g by
recycling reactants, changing conditions to
increase yield
• SAFETY: Need to be considered when high
temps/pressures are used, or if
reactants/products are toxic or flammable

Entropy
• DEFINITION: Measure of disorder
• ZERO ENTROPY: Perfectly crystalline solid at 0K in
temperature
• 2ND LAW OF THERMODYNAMICS: Entropy always increases
• TOTAL ENTROPY = entropy of system + entropy of
surroundings
• ENTROPY OF SYSTEM = entropy of products – entropy of
reactants (values found in data book)
• ENTROPY OF SURROUNDINGS = -enthalpy change/temp(K)
• UNITS: JK-1mol-1

Factors affecting entropy
• PHYSICAL STATE: Entropy of solid < entropy of liquid < entropy of
gas  particles get further apart, so there are more possibilities for
their position in space
• DISSOLVING: Entropy increases if a solid is dissolved, entropy
decreases if a gas is dissolved, entropy can either increase or
decrease if a liquid is dissolved (see section on dissolving)
• NUMBER OF PARTICLES: More particles means higher entropy
because there are more possibilities for the particles arrangement
in space
• TEMPERATURE: Increase temp increases entropy because it
increases the quanta of energy of particles, so there are more
possible distributions of the particles
• CHANGE OF STATE: Rapid change in entropy because particles move
further apart/closer together

Feasibility
• TOTAL ENTROPY: Must increase for a reaction
to be feasible
• INCREASING TEMP: Increases entropy, so can
be used to make a reaction feasible

Enthalpies
• ENTHALPY OF SOLUTION: Enthalpy change when
1 mol of solute is dissolved in sufficient solvent to
produce an infinitely dilute solution
• LATTICE ENTHALPY: Enthalpy change when 1 mol
of a solid ionic compound is produced from
gaseous ions that start infinitely far apart
• ENTHALPY OF HYDRATION: Enthalpy change
when 1 mol of aqueous ions is formed from
gaseous ions
• ENTHALPY OF SOLUTION = Sum of enthalpies of
hydration – lattice enthaply

Factors affecting lattice enthalpy and
enthalpy of hydration
• CHARGE OF IONS: Larger charge on ions
increases lattice enthalpy/hydration enthalpy
• IONIC RADII: Larger ionic radii decreases
lattice enthalpy/hydration enthalpy

Measuring reaction rates
• COLORIMETRY: Measures change in intensity of
colour
• CLOCK REACTIONS: Time taken for a particular
amount of reactant to react//product to be
formed
• MASS CHANGE/VOLUME CHANGE: Used for gas
reactants/products
• TITRIMETRIC ANALYSIS: Measures changes in
conc of reactant/product when one is acid, alkali
or iodine by reacting with a known volume of
standard solution to neutralise

Rate equations
• AVERAGE RATE = change in conc/change time
• RATE = k[A]x[B]y
• K = rate constant, constant at a particular
temp
• [A] AND [B] = concs of substances A and B
• X AND Y = partial orders
• OVERALL ORDER = x + y

Rate-conc graphs
• RATE: y-axis
• CONC: x-axis
• 0 ORDER: Staight horizontal line = 0 order
• 1ST ORDER: Staight line, positive graident
through origin = 1 order
• 2ND ORDER: Parabola curve, positive gradient
through origin = 2 order

Conc-time graphs
• CONC: y-axis
• TIME: x-axis
• 0 ORDER: Straight line, negative gradient = 0
order
• 1ST ORDER: Curve, negative gradient, constant
half lives = 1 order
• 2ND ORDER: Curve, negative gradient, increasing
half lives = 2 order
• HALF LIFE: Time taken for reactant conc to fall to
half it’s initial value

Effect of temp on rate
• TEMP INCREASES: More molecules have
activation energy  rate constant increases 
rate of reaction increases
• ARRHENIUS EQUATION: Shows relationship
between rate constant and temp in Kelvin
• LOG FORM OF ARRHENIUS = lnk = -Ea/RT + c
• R = gas constant
• FINDING EA: Graph plotted with lnk on y-axis, 1/T
on x-axis  gradient = -Ea/R
• EA EQUATION: So Ea = R x -gradient

Rate-determining step
• RDS: Slowest step of reaction mechanism
• RATE EQUATION: Molecules involved shown
by rate equation
• PARTIAL ORDERS: Number of mols of
reactants shown by partial orders of rate
equation

Nucleophilic substitution  SN1
• TYPE OF RX:Tertiary halogenoalkanes
• OVERALL ORDER: First order rate equation
• RDS: C-X bond breaking is rate determining
step
• FAST STEP: C+ being attacked by OH- is fast
step
• RATE = k[RX]

Nucleophilic substitution  SN2
• TYPE OF RX: Primary halogenalkanes
• OVERALL ORDER: Second order rate equation
• RDS: Single step  only rate-determining step
• RATE = k[RX][OH-]

Activation energy
• ACTIVATION ENERGY: Minimum energy needed by reactant
particles before products can form
• EXOTHERMIC: Energy produced
• ENDOTHERMIC: Energy required
• CATALYSTS: Provide an alternative reaction pathway,
lowering activation energy
• HOMOGENEOUS CATALYST: In same physical state as
reactants
• HETEROGENEOUS CATALYST: In different state to reactants
• RECYCLING: Catalysts not part of the products of reaction
so can by recovered and reused

Chemistry Edexcel Unit 4.pptx

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Chemistry Edexcel Unit 4.pptx