OCR Chemistry AS Level Chains, energy and resources

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  • Created on: 13-12-11 19:55
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Chains, Energy and Resources
Representing formulae of organic compounds
Empirical formula ­ The simplest whole-number ratio of atoms of each
element present in a compound.
Molecular formula ­ The actual number of each element in a molecule.
General formula ­ The simplest algebraic formula of a member of the
homologous series, i.e. for an alkane: CnH2n+2
Structural formula ­ A formula showing the minimal detail for the
arrangement of atoms in a molecule.
Displayed formula ­ A formula showing the relative positioning of all the atoms
in a molecule and the bonds between them.
Skeletal formula ­ A simplified organic formula, with hydrogen atoms removed
from alkyl chains, leaving just a carbon skeleton and associated functional
groups.
No. Of Carbons Name
1 Methane
2 Ethane
3 Propane
4 Butane
5 Pentane
6 Hexane
7 Heptane
8 Octane
9 Nonane
10 Decane
IUPAC Rules for naming Alkanes
1. Find and name the longest continuous carbon chain.
2. Identify and name groups attached to this chain.
3. Number the chain consecutively; starting at the end nearest a substituent
group or that will give the lowest total numbers in the final name.
4. Designate the location of each substituent group by an appropriate number.
5. Assign the prefix di, tri, tetra etc. To indicate how many of each type of
substituent there are.
6. Assemble the name, listing groups in alphabetical order.

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Isomerism
Structural isomers: Molecules with the same molecular formula but with different
structural arrangements of atoms.
E/Z isomerism: A type of stereoisomerism in which different groups attached to each
carbon of a C=C double bond may be arranged differently in space because of the
restricted rotation of the C=C bond.
Z: Zey are on the same side.
E: They are on opposite sides.…read more

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Substitution - one on ­ one off -1 atom is exchanged for another
Elimination ­ 1 = 1 + 1 a molecule is eliminated from a larger molecule
Rearrangement ­ 1 = same molecular formula, different structural
arrangement (isomers)
Radical substitution-Alkanes
Electrophilic Addition-Alkenes…read more

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Alcohols
Primary alcohol ----------- aldehyde ---------- carboxylic acid
Secondary alcohol ----------- ketone
Tertiary alcohol---------- Nothing!
Create an alcohol - hydrate an alkene with steam
Fermentation
Hydrolysis of a halogenoalkane ­ nuclear substitution
Steam Hydration
Fermentation
C6H12O6 2 C2H5OH + 2 CO2
Hydrolysis of halogenoalkane ­nuclear substitution…read more

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Esterification of alcohols
An ester is created by reacting an alcohol with a carboxylic acid. It is refluxed with
H2SO4 added as a catalyst (H+ catalyst)
Naming an ester:
Take the alcohol name as the first name. (e.g. methyl)
The first part of the second name is the acid. (e.g.ethan)
Then stick `oate' on the end!
Uses of halogenoalkanes
Chloroethene and tetrafluoroethene are used to produce the plastics PVC and PTFE.…read more

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Exothermic Endothermic
Gives out energy Absorbs
H is negative H is positive
Working out enthalpy changes
E=mcT
m=mass of water (g)
c=specific heat capacity of water (4.18J g-1K-1)
T=the change in temperature of the water
This is divided by the number of moles of fuel to get enthalpy change of combustion.
Hess's Law
Enthalpies of formation
1 is going against the arrow so we minus it and 3 is with the arrow so we add it.…read more

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Enthalpy changes of combustion
H of the reactants is going with the arrow so we add and H of the products is going
against so we minus.
Reaction Rates
Increasing concentration means the particles are closer together so they will
collide more often. More collisions mean more chances to react.
Increasing pressure in gases means the particles are closer together and
therefore are more likely to collide successfully.
Increasing temperatures means more molecules will have enough energy to
overcome activation energy.…read more

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The presence of a catalyst lowers activation energy which means more
molecules have enough energy to overcome activation energy.
Dynamic Equilibrium
Le Chatelier's principle: When a system in dynamic equilibrium is subjected to
change, the position of equilibrium will shift to minimise the change.
Increase concentration of reactants and the equilibrium will make more
products.
Increase pressure and the equilibrium will shift to the side with the fewer gas
molecules.…read more

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As the bonds in these compounds vibrate more, the molecules gain kinetic energy
which increases the temperature of these gases. They can also transfer the kinetic
energy to other molecules in the atmosphere by collision, so the whole atmosphere
gets warmer. These gases are called greenhouse gases!
The "greenhouse effect" of a gas is dependent on both its atmospheric concentration
and its ability to absorb infrared radiation.
Kyoto Protocol was signed by industrialised countries that promised to reduce their
greenhouse gas emissions to agreed levels.…read more

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