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UNIT 2: F322
UNIT 2 Chains, Energy and Resources revision guide
Module 1: Basic Concepts and Hydrocarbons
2.1.1 Basic Concepts
2.1.2 Alkanes
2.1.3 Alkenes
Module 2: Alcohols, Halogenoalkanes and Analysis
2.2.1 Alcohols
2.2.2 Halogenoalkanes
2.2.3 Modern Analytical Techniques
Module 3: Energy
2.3.1 Enthalpy Changes
2.3.2 Rates and Equilibrium
Module 4: Resources
2.4.1 Chemistry of the Air
2.4.2 Green Chemistry
Module 1
Leahanne SummersPage 1

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Basic Concepts
Formulae of Organic Compounds
- Empirical Formula: The simplest whole-number ratio of atoms of each element
present in a compound.
- Molecular Formula: The number of atoms of each element in a molecule, e.g.
propane C3H8.
- General Formula: The simplest algebraic formula of a member of a homologous
series. For example, the general formula of the alkanes is CnH2n+2.
- Structural Formula: A formula showing the minimal detail for the arrangement of
atoms in a molecule, e.g.…read more

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- Homologous series: A series of organic compounds with the same functional
group, but with each successive member differing by CH2.
- Functional group: The part of the organic molecule responsible for its chemical
Need to know first 10 members of the alkanes homologous series:
Methane, Ethane, Propane, Butane, Pentane, Hexane, Heptane, Octane, Nonane, Decane.…read more

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Structural isomers: Molecules with the same molecular formula but with different
structural arrangements of atoms.
- Stereoisomers: Compounds with the same structural formula but with different
arrangement of the atoms in space.
- E/Z isomerism: A type of stereoisomerism in which different groups attached to
each C=C double bond may be arranged differently in space because of the restricted
rotation of the C=C bond.…read more

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Atom Economy
molecular mass of the desired products
atom economy =
sum of molecular masses of all products ×100
- All addition reactions have a 100% atom economy
- The higher the atom economy the less waste products
Processes may have high % yield but this can be slow and very costly, therefore there are
compromises between the % yield and the atom economy.
2.1.2 Alkanes
Alkanes and cycloalkanes are saturated hydrocarbons.…read more

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Effect of chain length
- As the chain length increases, so does the boiling point.
- This is because the intermolecular forces between molecules get stronger.
- In longer alkanes, there are more points of contact between the molecules leading
to more van der Waals forces.
- Therefore it takes more energy (heat) to separate the molecules.
Effect of branching
- The more branching the lower the boiling point of a molecule with the same
molecular mass.…read more

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Catalyst: a substance that increases the rate of a chemical reaction without being
used up in the process
Short chained alkanes are in higher demand, therefore cracking is a
process used to fulfil this demand.
- Short chained alkanes are used as fuels.
- Short chained alkenes are in high demand for polymer production.
Cracking is a process that takes place at around 450°c and a zeolite catalyst is used.…read more

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Producing cyclic hydrocarbons
Aliphatic hydrocarbons can be converted into cyclic or aromatic hydrocarbons in a process
sometimes known as reforming.
Improving fuels
- Research octane number (RON) rates how well a fuel burns. Fuels with near 100
ratings burn more efficiently. Heptane burns poorly and has an octane rating of zero.
- Branched and cyclic alkanes promote more efficient combustion than straight chains.
- Hydrogen produced during reforming is used in other chemical processes such as
ammonia and margarine production.…read more

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Halogenation of alkanes
Alkanes react with halogens in the presence of UV radiation or at a temperature of about
300°c. For example methane reacts with chlorine to produce chloromethane:
CH4 + Cl2 CH3Cl + HCl
This is radical substitution. Covalent bonds are broken by Homolytic fission to form
radicals. A hydrogen atom in the alkane is substituted by a halogen atom.
Mechanism for chlorination
- Initiation: the first step in radical substitution in which free radicals are generated by
ultraviolet light.…read more

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Properties of Alkanes
- Pi( )-bond: the reactive part of a double bond formed above and below the plane of
the bonded atoms by the sideways overlap of p-orbitals.
- Sigma( )-bond
In the formation of the double bond:
- A -bond is formed directly between to carbon atoms by the overlap of orbitals.…read more



Thank you so much. These are so helpful, well written and useful. 


This was soooooo helpful 


Shaur Budree



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