Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Chemistry
Unit 2

Definitions
•
•
•
•
•
•

Formulas:
Molecular: the actual amount of atoms of each element in a molecule
...

Structural: shows the atoms carbon by carbon, with the attached hydrogen's
and functional groups
...

Displayed: shows how all atoms are arranged and the bonds between them
...


• Homologous Series: a series of compounds that belong to the same family
and have the same general formula and functional group, but a different
length carbon chain
...


Isomers
• Atoms can rotate as much as they want around single carbon-carbon bonds
...

They have similar chemical properties but physical properties, like boiling
point, are different due to the change of the molecular shape
...

They have different physical properties and chemical properties may also be
different, but not always
...

They have very different physical and chemical properties
...

•
•

E/Z Isomers
E-Isomer: two carbon atoms have ‘higher priority groups’ on opposite sides
...

High priority groups are decided by the atomic number or mass of the elements
involved: a higher atomic number, the higher the priority
...

Trans-Isomer: two identical groups on opposite sides
...
There must be two hydrogen's, and two
identical groups
...

• Percentage Yield Equation:

• Percentage Atom Economy Equation:

Alkanes
General Formula: CnH2n+2

Functional Group:

• Alkanes are saturated as they only have
single bonds between the carbon atoms
...


•Alkanes make excellent fuels: this is because
although some energy is required to break
the covalent bonds, more energy is released
when the bonds of the new products are
formed
...

Bond angle: 109
...

• They have relatively high boiling points
...

• Van Der Waals forces hold the separate molecules together
...

• The branched-chain alkanes have lower boiling points compared to
straight-chain alkane due to a decreased surface area in the branchedchain
...

2
...


4
...


Put a 2 in front of the alkane molecule
Place the number of hydrogen's that are in the alkane in front of the water molecule
...

Add up all the oxygen's, half the amount, place this number in front of the oxygen
molecule
...


•

Complete combustion produces carbon dioxide and water
...
g
...

e
...
2 C4H10 + 9 02 --> 8 C0 + 10 H20

Rules for Naming Alkanes
(Alkane Nomenclature)
1
...


3
...

5
...

Name the side chains:
E
...
One carbon in the group: Methyl
...

Multiple side chains will use prefixes: 2 is di, 3 is tri, 4 is tetra
...

When there are two different side chains, name them in alphabetical order
...

Dashes are used between numbers and words
...

• Crude oil is vaporised at 350˚C
• Vaporised crude oil goes into the bottom of the fractionating column and
rises up through trays depending on the boiling points of the different
hydrocarbons
...

• As vapour rises up the column and cools, a temperature gradient is created
...

• The smallest hydrocarbons don’t condense, instead they are drawn off as
gases
...

• Cracking is used as light fractions are more useful and desirable
...
This creates an alkane and an alkene
...


Octane Ratings
• How a petrol engine works:
1
...

2
...
This creates a tiny explosion
...
The explosion drives the piston up and turns the crankshaft, which drives the
car
...

The higher the number, the less likely it’ll auto-ignite
...

100% 2,2,4-trimethylpentane has an octane rating of 100
...


Isomerism and Reforming
•
•
•
•

Isomerism
This is the conversion of a straight-chain alkane into a branched one
...

A molecular sieve is used to separate isomers
...


Reforming
• This is the conversion of a straight-chain alkane into a cyclic one
...


Heterolytic and Homolytic Fission
• Heterolytic fission: atoms with different charges are produced
...

These free radicals are very reactive
...


Free Radical Substitution
Example: Methane and Chlorine
The reaction wanted in order to produce chloromethane: CH4 + Cl2CH3Cl + HCl
Step One: Initiation
The first reaction is initiated by UV light breaking the bonds of a chlorine molecule to
produce two free radicals
...


Step Three: Termination
These are reactions which remove free radicals from the system without replacing them
by new ones
...


Halogenoalkanes
•

Halogenoalkane: an alkane with at least one halogen atom
...

They are stable, volatile, non-flammable and non-toxic
...
g
...

Scientists then realised CFC’s destroyed the ozone layer
...

Chlorotrifluoromethane
...

Some ozone-destroying halogenoalkanes were permitted – those in medical inhalers and in
fire extinguishers in submarines
...


•
•
•
•
•
•

Hydrochlorofluorocarbons (HCFC’s) and Hydrofluorocarbons (HFC’s):
These are temporary alternatives to CFC’s
...

HFC’s don’t affect the ozone layer – no chlorine
...

Some hydrocarbons are used in fridges are also greenhouse gases
...

Ammonia is used in fridges and freezers
...


•
•
•

Polymer halogenoalkanes:
Plastics PVC (from chloroethene)
Plastics PTFE (from tetrafluoroethene)

•

Nucleophilic Substitution
• Halogens are much more electronegative than carbon – the bond is polar
...

•
•
•
•
•

Nucleophiles:
:CN- (cyanide ion)
:NH3 (ammonia)
:OH- (hydroxide ion)
Water is a nucleophile, but it reacts slowly
...

The lone pair creates a new bone between the nucleophile and the carbon
...

The electron pair from the carbon-halogen bond are taken by the halogen and
become a lone pair
...

General equation: R-X + -OH  ROH + XConditions: Reflux
...


• Water can be used as a nucleophile: R-X + H2O  R-OH + H3O+ + X• If you put the mixture in silver nitrate, the silver ions will react with the halide
ions – gives a silver halide precipitate
...

• Put a cross under each flask and measure how long it takes until you can’t see
the cross anymore
...

• If this test is done with an alkali nucleophile, you must:
• Add NaOH to the halogenoalkane, the OH ion acts as the nucleophile
...


Alkenes
General Formula: CnH2n

Functional Group:

• Alkenes are unsaturated as they have
double carbon bonds
...


•Alkenes are isomers of cyclic compounds as
they have the same general formula
...
This
creates a Sigma (σ) bond
...
This is when the p-orbitals overlap sideways
...
This means that a double bond
is not twice as strong as a single bond
...
This
makes alkenes very reactive
...

• A double bond has a trigonal planar shape
...


2
...

4
...

4
...


Find and name the longest carbon chain, unless there is more than one double bond
in a carbon chain
...

If the alkene has two double bonds, the suffix becomes –diene instead of just –ene
...
g
...
g
...

Two carbons in the group: Ethyl, and so on
...

When necessary use the lowest number to give the location of each side chain
...


Commas are used between numbers
...


Electrophilic Addition
• Electrophile: a species that accepts an electron-pair in a chemical reaction
...


Example of Electrophilic Addition
Ethene and HBr
1
...
That means that the bonding pair
of electrons is pulled towards the bromine
end of the bond, and so the hydrogen
bromide molecule is polar
...
g
...
This causes
an induced dipole
...
The structure of ethene is shown in the diagram on the
right
...


3
...

4
...

In the process, the electrons in the H-Br bond are repelled down until they are entirely on
the bromine atom, producing a bromide ion
...
That leaves you with these two ions at this half-way stage of
the reaction:
The ion with a positive charge on the carbon atom is called
a carbocation
...
In the second stage of the mechanism, the lone pair of electrons on the bromide ion
is strongly attracted to the positive carbon and moves towards it until a bond is formed
...


Reactions of Alkenes
• Testing for unsaturation:
• Alkenes react with halogens to form dihalogenoalkanes
...

• H2C=CH2 + Br2  CH2BrCH2Br
•
•
•
•

Producing alkanes:
Ethene will react with hydrogen gas to produce ethane
...

H2C=CH2 + H2  CH3CH3

• Margarine’s made by hydrogenating unsaturated vegetable oils – removing
double bonds increases melting point
...

• The individual alkenes are called monomers
...

• Poly(chloroethene) is used for making
water pipes, insulation on wires and as
building materials
...


Disposing of Polymers
•

Synthetic polymers: are widespread and have many advantages – they’re very unreactive and
therefore don’t rot (this is also a problem – not biodegradable)
...

Used when:
Plastic is difficult to separate from other waste
...

Plastic is too difficult to recycle
...

After sorting plastics, they can be melted and remoulded – others can be cracked
...


•
•
•
•

Burning waste plastic 
Heat from this process can be used to generate electricity
...

Waste gases are passed through scrubbers to neutralise them
...

Biodegradable polymers can be made from starch or the hydrocarbon isoprene
...


•
•
•
•

Advantages of using renewable materials:
Won’t run out
...

Save energy compared to oil-based plastics
...

Still need to collect and separate them
...


•
•
•
•
•
•

Other things scientists can do:
Photodegradable plastics
...

Use processes with higher atom economy
...

Develop more efficient ways of sorting and recycling polymers
...

If there are two OH groups, the name ends in –diol
...


•

All alcohols contain a polar hydroxyl group – a δ- charge on the O and a δ+ charge
on the H
...


•

•
•
•
•

Mixing alcohol and water hydrogen bonds to form between them
...

Larger alcohols won’t mix easily with water because it’s mostly made of a non-polar
carbon chain
...


•

Alcohols have relatively high boiling points due to hydrogen bonds
...

Conditions: 300˚c and 60 atm
...

The reaction is reversible, and the yield is low – about 5%
...

H2C=CH2 (g) + H2O (g)  CH3CH2OH (g)

•

•
•
•
•
•

Industrial production of ethanol by fermentation
...

At 15% ethanol, the yeast dies
...

C6H12O6 (aq)  2CH3CH2OH (g) + 2CO2 (g)

Reactions of Alcohols
• Dehydration of alcohols:
• Catalyst: either concentrated sulfuric acid or concentrated phosphoric acid
...


Functional Group

Carboxylic Acids
• General formula: CnH2nO2
• Suffix: -oic and ‘acid’

Functional Group

• E
...
Propanoic acid:

Oxidising Alcohols
•
•

Oxidation through burning:
Alcohol + Oxygen  Carbon Dioxide + Water

•
•
•

Oxidation using an oxidising agent [O]:
[O] = Acidified Potassium Dichromate: K2Cr2O7/H2SO4
Orange dichromate(VI) ion is reduced to the green chromium(III) ion
...

Aldehyde + [O]  Carboxylic Acid
Conditions: Heat and under reflux conditions
...


•

Tertiary alcohols can only be oxidised through burning
...
g
...
g
...

• The water is produced from the -H in the alcohol’s functional group and the
-OH in the carboxylic acid’s functional group
...

• Drawing esters: carboxylic acid structure is drawn first, then the alcohol
...

• Bonds between different atoms and places absorb different frequencies
...


Mass Spectroscopy
•
1
...

3
...

•
•
•
•
•
•

First the molecule is vaporised
...

Acceleration: ions are accelerated into a magnetic field so that they all have the
same kinetic energy
...
The
lighter they are, and the more positive, the more they’re deflected
...

The bombarding of electrons makes some of the molecular ions break up into
fragments – makes a fragmentation pattern on the spectrum
...

Every compound produces a different mass spectrum – like a fingerprint
...

Mass spectrometry can be used to measure pollutants
...


•

Standard Enthalpy Change of Formation: the enthalpy change when 1 mole of a
compound is formed from its elements in their standard states under standard
conditions
...


•

Average Bond Enthalpy: the bond enthalpy when 1 mole of gaseous covalent bonds
are broken
...


Enthalpy Changes
•
•
•
•
•

Standard conditions:
100 kPa (1 atm)
298 K (25˚c)
1M
Everything in their standard states
...


• Exothermic: reactions give out energy to their surroundings so the products
have less energy than the reactants
...

• Endothermic: reactions take in energy from their surroundings so the
products have more energy than the reactants
...


Bond Enthalpies
• Bond breaking is endothermic (ΔH+)
• Bond forming is exothermic (ΔH-)
• Bond dissociation enthalpy: the amount of energy you need per mole to break
bond attraction in gaseous compounds
...

• Enthalpy change of a reaction is the overall effect of these two changes
...

• Enthalpy change of a reaction = total energy absorbed – total energy released
...

• The change in temperature
...

• For combustion reactions, a copper calorimeter containing a known mass of
water is used – record the temperature change of water
...

M = mass (g) of the solution/water in calorimeter
...
18 j/g/k)
ΔT = change in temperature of solution/water
...
Calculate q=mcΔT
2
...

3
...

4
...

2
...


Calculating enthalpy change of a reaction:
Instead of calculating enthalpy change per mole, find the enthalpy change for the
number of moles in the balanced equation
...

Calculate the number of moles of one of the reactants
...

ΔHr = Q/N x number of moles in equation

Hess’ Law
•

Hess’ law: the total enthalpy change of a reaction is always the same, no matter
which route is taken
...

Enthalpy change of formation  The intermediate products are the constituent
elements
...
6 + 90
...
5

Reaction Rates
•

Collision theory: a reaction won’t take place between two particles unless they collide in
the right direction with at least a certain minimum amount of kinetic movement energy
...


Maxwell-Boltzmann Distribution
•
•

•

Effect of temperature:
Increase the temperature, the kinetic
energy also increases
...

This pushes the curve to the right
...

The curve rises as there’s more particles
...


•

Catalysts
• Catalyst: increases the rate of reaction by providing an alternative reaction
pathway with a lower activation energy – they’re chemically unchanged by the
end so only a tiny amount is needed
...

• The broken reactant molecules form product molecules and desorb the surface
of the catalyst
...

• With a catalyst present, the molecules still have the same amount of energy so
the Maxwell-Boltzmann distribution curve is unchanged – but the catalyst shifts
the activation energy line to the left
...
t
...

• Energy is saved when using catalysts – less carbon dioxide is produced and fossil
fuels are preserved – this reduces waste
...


• All catalysts need to be disposed of – many contain toxic compounds that may
leach into the soil if in a landfill
...


Reversible Reactions
• Dynamic equilibrium: the forward and backward reaction are going at the same
rate so the concentrations of the reactants and products don’t change – can
only happen in a closed system
...

• If it moves to the left, the backwards reaction is favoured so you’ll get more
reactants and vice versa
...

• Catalysts have no effect – only increase the rate of the reaction
...

Decreasing concentrations has the opposite effect
...

Increasing pressure moves the equilibrium to the side with fewer gas molecules in
order to reduce the pressure
...


•
•
•
•
•

Changing temperature 
Increasing temperature means adding heat energy
...

Decreasing temperature removes heat energy
...


Ethanol Production

•
•
•
•

Conditions:
60-70 atm
300˚c
Phosphoric acid catalyst

• Exothermic reaction – lower temperature favours forward reaction – better
yield but slower reaction rate – 300˚c is a compromise
...

• Only small proportion of ethene reacts each time the gases pass through the
catalyst – ethene is separated from liquid ethanol and recycled – 95% of ethene
is eventually converted
...


•
•
•

Chemicals are as non-toxic as possible 
Lead used to be used in pain, petrol and for soldering – now they use lead-free compounds
...

Dry cleaners used to use chlorinated hydrocarbons – known to be carcinogenic – safer
alternatives are now used
...


•
•
•
•
•

Using renewable energy sources 
Many chemical processes use a lot of energy from fossil fuels
...

Solar power, wind power, geothermal or wave energy
...


Green Chemistry
•
•
•

Ensuring products/waste are biodegradable/recyclable 
Conserving raw materials is essential
...


•
•
•

Disadvantages of greener chemistry 
Example (biofuel):
Less land to grow food, larger companies may buy most fertile land – farmers are
forced to have land with poorer crop yields
...


•

•
•
•

•

The need for international cooperation 
Pollution travels so cooperation is vital
...

‘Montreal Protocol’: the phasing out of production of substances that damage the
ozone layer
...

Earth re-emits it as infrared radiation
...

Main greenhouse gases 
Water vapour, carbon dioxide and methane
...

The contribution of a gas depends on 
How much IR one molecule absorbs
...

Residence time – how long the gas stays in the atmosphere
...


Global Warming
• Scientists collect data to provide evidence for if and why global warming and
climate change are happening – from air samples and sea water samples
...

• Kyoto Protocol: industrialised countries promise to reduce their greenhouse gas
emissions to agreed levels
...

• CCS involves removing waste carbon dioxide and
...

• Store it deep underground
...


The Ozone Layer
•
•

Ozone layer: stratosphere of the atmosphere – contains most of the ozone
molecules
...


•
•
•

O2 + hv  O· + O·
O2 + O·  O3
Ozone is constantly being destroyed and replaced
...

These increase in frequency and energy
...

UVA and UVB can lead to skin cancer – they break down collagen fibres in the skin
causing it to age faster
...


•
•

1970/1980’s: Scientists discovered the ozone layer was thinning – allows harmful
UVB to reach earth
...

CF3Cl + hv  CF3· + Cl·
These free radicals destroy ozone molecules and regenerate to destroy more
...

Other substances are used which have ozone depleting properties
...


• Equations for ozone depletion:
• R represents a free radical (Cl· or NO·)
1
...
RO + O·  R + O2
•
•

Free radical regenerates by the end so it acts as a catalyst
...

Binds to haemoglobin so oxygen cannot
...

Oxides of nitrogen are produced when the high pressure and temperature in a car engine cause
nitrogen and oxygen from the air to react
...


•

Air Pollution

• Catalytic converters 
• Converts pollutants into harmless gases – water vapour, nitrogen or carbon dioxide
...
Reactant molecules arrive at surface and bond with catalyst – adsorption
...
Bonds weaken and break to form free radicals – react to form new molecules
...
New molecules detach – desorption
...

Monitoring carbon monoxide 
A sample of air is drawn into spectrometer – a beam of IR radiation is passed through
...

The difference in amount absorbed is the amount of carbon monoxide present

---