UNIT 2 OCR CHEM - Only 4 pages long!:-D

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Chemistry ­ Condensed AS:2 Notes
Empirical Formula: The smallest (whole number) ratio of atoms of an element in a compound.
Molecular Formula: The actual number of atoms of an element present in a compound.
General Formula: The algebraic formula for molecules in a homologous series ­ ie.
CnH2n = Alkene CnH2n + 2 = Alkane
Structural Formula: A formula for showing the minimal amount of detail with regards to the arrangement of atoms in a
Displayed formula: A Formula for showing the arrangements of atoms in a molecule, and the different bonds that are
Skeletal Formula: Shows only the carbon skeleton and the arrangements of any functional or alkyl groups ­ doesn't show
presence of Hydrogen atoms.
Structural Isomers: Molecules with the same Molecular Formula (Definition above), but with different structural
arrangements of atoms.
E/Z (Cis / Trans) Isomerism: A type of stereoisomerism in which different groups attached to the carbons of a C=C double
bond may only be arranged two different ways in space ­ due to the lack of rotation around the double bond.
E ­ They are on opposite sides
Z ­ They are on the same side
Bond Enthalpy: The enthalpy change that takes place when breaking a homolytic fission of 1 mol of a given bond in the
molecules of a gaseous species.
Enthalpy change of combustion: The enthalpy change that takes place when 1 mol of a substance reacts completely with
oxygen. (Under standard conditions*) (Whilst all reactants and products are in standard states)
Enthalpy change of formation: The enthalpy change which takes place when 1 mol of a compound is formed from its
constituents. (Under standard conditions*) (Whilst all reactants and products are in standard states)
Enthalpy change of reaction: The enthalpy change that accompanies a reaction in the molar quantities expressed in a
chemical equation. (Under standard conditions*) (Whilst all reactants and products are in their standard states)
*Standard conditions: 25 C, (298K) 100kPa (1 atm)
Le Chatelier's Principle: When a system in a dynamic equilibrium is subject to change, the position of equilibrium will shift in
an attempt to minimise the change.
Naming Alkanes
1. Find and name the longest carbon chain
2. Identify and name groups attached
3. Number the chain ­ beginning with the carbon
nearest to a constituent group
4. Designate the location of each substituent
group by an appropriate number
5. Assign the prefix, (di, tri, tetra, ect) to indicate
how many of each type of substituent there are
6. Assemble the name ­ listing groups alphabetically
Calculations ­ Percentage Yield and Atom Economy
Percentage Yield = Actual Yield x 100
Theoretical Yield
Atom Economy = Molecular mass of desired products x100
Sum of molecular masses of all products
Kate Baker 2012

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Reaction Mechanisms:
Breaking Bonds:
Homolysis: X ­ X X· + X·
Heterolysis: X ­ X X- + X+
Types of Organic Species:
Radicals: Has an unpaired electron, so is highly reactive
Electrophiles: Accepts a pair of electrons to form a bond
Neutrophiles: Donates a pair of electrons to form a bond
Types of Organic Reaction:
Addition: 1 + 1 Only one product ­ 100% Atom economy
Substitution: One atom is added, one atom is removed (An exchange of sorts)
Elimination: One reactant, two products ­…read more

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M+ = Molecular ion peak. This is the last line on the spectrum (unless
a smaller one is shown), and is the molecular mass.
29 = CH3-CH2+
43 = C3H7+
58 = C4H10+
Enthalpy (H)
Exothermic: Endothermic:
-Gives out energy -Takes in energy
-Reactants become -Reactants become
more stable and lose less stable and gain
energy energy
- H is always negative - H is always
Calculations for enthalpy change:
E (Energy) = m(Mass of water)c(Specific heat capacity (4.…read more

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TEMPERATURE ­ Equilibrium will shift to the endothermic direction (Shift to absorb heat)
Low temperature = Slow reaction, cheap
High temperature = Fast reaction, expensive (fuel costs)
High Pressure = Expensive equipment, side reactions and danger
Low Pressure = Slow reaction, safe, cheap, no training costs
Global Warming
Infared radiation is absorbed by C=O, O-H and CH2 bonds in molecules. Absorbing this causes the bonds to
gain energy and vibrate.…read more




This is such a great revision tool. I always struggle with deciding what I do and do not need to know/learn, so this has helped me a lot thanks so much! <3

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