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Organic Groups
Alkanes: Saturated (CnH2n+2). Contain single bonds. Every carbon atom has 4 bonds with other atoms. You can get
Alkenes: Unsaturated (CnH2n).Contain at least one C=C bond. Molecules with double bonds are unsaturated
because they can make more bonds with extra atoms in additional reactions.
Cycloalkanes: Saturated (CnH2n). They have a ring of carbon atoms with two hydrogen's attached to each carbon
atom.
Arenes: Unsaturated. They're aromatic (one or more benzene rings). It's more stable because the double bonds are
delocalised around the carbon ring. That's why there's a circle inside it.
Alcohols: (CnH2n+1OH).
Ethers: C-O-C. Prefix: shorter chain +oxy. Suffix: longer chain. Ethers and alcohols can be isomers of each other.
Homologous Prefix/Suffi Example
Series x
Alkanes -ane Propane
Naming Compounds:
Side chains in -yl Methyl
1. Count the carbon atoms in the longest chain.
branched Propane 2. The main functional group of the molecule usually gives you the
alkanes end of the name (suffix).
Alkenes -ene Propene
3. Number the carbons in the longest chain so that the carbon with
the main functional group attached has the lowest possible
Alcohols -anol propanol
number.
4. Write the carbon number that the functional group is on before
the suffix e.g. pentan -2- ol.
Cycloalkanes Cyclo- - cyclopropane
ane 5. Any side chains or less important functional groups are added as
prefixes. Put them in alphabetical order, with the number of the
Arenes -yl Methyl
carbon atom each is attached to e.g. 3,ethyl -2,4 dimethyl pentan
benzene Benzene
-2- ol.
Ethers -oxy- Methoxy
Propane…read more

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Isomers
Isomers have the same molecular formula, but different arrangements of atoms. There are three types of
structural isomerism.
Chain Isomerism (different carbon chains): The chain lengths are different. These isomers will have similar
chemical properties but their physical properties (e.g. boiling point) will differ. Often seen in alkanes.
Positional Isomerism Different positions of functional group): The same functional group appears in different
positions. This is often seen in alcohols. These have different physical properties and the chemical properties may
differ too.
Functional Group Isomerism (different functional groups): The molecular formula are the same but the functional
groups are different. This can be seen in alcohols and ethers. These have very different physical and chemical
properties.…read more

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Enthalpy and Entropy
Enthalpy is the energy that is stored in chemicals. The enthalpy change is the difference between the energy
stored in products of a reaction and the energy stored in reactants. Enthalpy change is represented by the symbol
(delta).
An exothermic reaction gives out energy to the surroundings. The temperature of the surroundings increase. H is
negative.
An endothermic reaction takes energy from the surroundings. The temperature of the surroundings decrease. H
is positive.
Enthalpy Changes:
When chemical reactions happen, some bonds are broken and some bonds are made. This'll cause a change in
enthalpy. The units of H are kJmol-1.
Changes in enthalpy are affected by temperature and pressure. Using standard conditions (temperature: 25C,
pressure: 1 atmosphere) means that all of the chemicals are used in there standard form e.g. oxygen under
standard conditions is a gas. HO shows elements were used under standard conditions.
(ENTHALPY CHANGE = BONDS BROKEN - BONDS MADE)
Entropy:
Is the measure of disorder. Particles will naturally move to give a substance the maximum possible entropy.
· Gases diffuse to fill all the available space because there are more ways of arranging particles in a bigger space.
· When something dissolves, the solute particles spread out into the solvent, the entropy increases.
· Increasing the number of particles increases entropy, a greater number of particles can be arranged in more
ways.
· A mixture of two different types of particles has more entropy than the same number of one type or particle.…read more

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Hess's Law
Hess's law sates that the total enthalpy change of a reaction is always the same, no matter which route is taken.
Example:
Compund Hf
Calculate the standard enthalpy change of combustion for ethanol.
C2H5OH -277
Formula: -A + B + C CO2 -394
H2O -286
C2H5OH + 3O2 2CO2 + 3H2O
-(-277) + (-394) + (-286) = -1369 kJmol-1…read more

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Auto-ignition
Auto ignition is spontaneous combustion. The octane number is a measure of the tendency of petrol to auto-
ignite. Auto-ignition in a petrol engine causes: a knocking sound, reduced engine performance and engine
damage. A higher octane number means a low tendency to auto-ignite.
· Short chained compounds have higher octane numbers.
· Branched compounds have a higher octane number.
· Cycloalkanes have higher octane numbers than straight chained alkanes.
· Arenes have higher octane numbers than cycloalkanes.
· Oxygenates have higher octane numbers than alkanes, that's why they're added to petrol to increase octane
numbers.
The petrochemical industry uses a number of different chemical reactions to increase octane numbers.
· Cracking: Shorter chains are made. It makes a shorter alkane and an alkene. A zeolite is used as a catalyst.
· Reforming: Alkanes are converted to cycloalkanes and hydrogen. Cycloalkanes are then converted to arenes
and hydrogen. Platinum is used as a catalyst.
· Isomerisation: More branched. Platinum is used as a catalyst.…read more

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