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CHEMISTRY A2 2022
Terms

Explanation

Enthalpy change of
atomisation, ∆H°atm

Enthalpy change when one mole of gaseous atoms is
formed from its element under standard conditions
(endothermic)

Enthalpy change of formation

Enthalpy change when one mole of an ionic compound is
formed from its elements in their standard states under
standard conditions (exothermic)

Lattice formation enthalpy
(lattice energy)

Energy change when one mole of an ionic compound is
formed from its gaseous ions under standard conditions
(exothermic)

Lattice dissociation enthalpy

Energy change when one mole of an ionic compound
dissociates to form its gaseous ions under standard
conditions (endothermic)

1st Ionisation energy

Energy required to remove one mole of gaseous
electrons from one mole of gaseous atoms to form one
mole of gaseous +1 ions under standard conditions
(endothermic)

1st Electron affinity, EA1

Enthalpy change when one mole of electrons is added to
one mole of gaseous atoms to form one mole of gaseous
-1 ions under standard conditions (exothermic)

2nd Electron affinity, EA2

Enthalpy change when one mole of electrons is added to
one mole of gaseous -1 ions to form one mole of
gaseous -2 ions under standard conditions (endothermic,
energy is needed to overcome the repulsion)

Ion polarisation

The distortion of the electron cloud of an
anion by a neighbouring cation
...


Polarising power

The ability of a cation to attract the electron cloud of an
anion and distort it
...


Entropy, S

Number of possible arrangements of particles and their
energy in a given system

Units:
∆H°reaction in kJmol-1
∆S° in JK-1mol-1
∆G° in kJmol-1
T in Kelvin (0°C = 273 K)

∆S°total = ∆S°system + ∆S°surrounding
∆𝐻°𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛
𝑇

∆S°surrounding = -

∆S°system = ∆S°product - ∆S°reactant
∆G° = -T∆S°total
∆G° = ∆H°reaction - T∆S°system

Electrolysis

The decomposition of an ionic compound when molten or
in aqueous solution by an electric current

Electrolyte

A molten ionic compound or an aqueous solution of ions
that is decomposed during electrolysis

Electrode

A rod of metal or carbon (graphite) which conducts
electricity to or from an electrolyte
Cathode - negative electrode (where reduction occurs)
Anode - positive electrode (where oxidation occurs)

Faraday, F

The quantity of electric charge carried by one mole of
electrons or one mole of singly charged ions
...
00 mol dm-3 H+ ions

Standard cell potential, E°cell

The difference in electrode potentials between two
half-cells under standard conditions
...
059
𝑍

log

[𝑜𝑥𝑖𝑑𝑖𝑠𝑒𝑑 𝑠𝑝𝑒𝑐𝑖𝑒𝑠]
[𝑟𝑒𝑑𝑢𝑐𝑒𝑑 𝑠𝑝𝑒𝑐𝑖𝑒𝑠]

E°cell = E°reduction - E°oxidation
E°cell = E°right - E°left
∆G° = -zFE°cell , a reaction is feasible if E°cell is positive

Bronsted-lowry acid

Substance that donates proton

Bronsted-lowry base

Substance that accepts proton

pH

Measure of concentration of H+ ion
pH = -log [H+]

Acid dissociation, Ka & pKa

pKa = -log Ka

Ionic product of H2O, Kw

Kw = [H+][OH-] = 1
...
g
...
g
...
g
...


Degenerate d orbitals

Orbitals are at the same energy level

Non-degenerate d-orbitals

Orbitals are at slightly different energy level

Stability constant, Kstab

Equilibrium constant for the formation of a complex ion
from its constituent ions in solution
The higher the value of Kstab, the further the reaction lies to
the right, the more stable the complex ion is

Disproportionation

A reaction where one substance undergoes both oxidation
and reduction
...


Electrophoresis

The separation of charged particles by their different rates
of movement in an electric field
Since amino acids are colourless, ninhydrin is added to
give colour to monitor its movement

Isoelectric point

The pH at which there is no overall charge on a particular
amino acid in aqueous solution

Addition polymerisation

A reaction in which monomers containing C=C bonds react
together to form long chain molecules called polymers

Condensation polymerisation

A reaction in which two organic molecules join together by
eliminating a small molecule such as H2O and HCl

Stationary phase

Immobile phase in chromatography that the mobile phase
passes over or through

Mobile phase

The solvent in the chromatography process which moves
through the column or the paper or the thin layer

TLC (Thin-layer
chromatography)

Stationary phase: silica gel (S2O3) / alumina (Al2O3) on a
solid support
Mobile phase: a polar or non-polar solvent

GLC (Gas-liquid
chromatography

Stationary phase: a high boiling point non-polar liquid on a
solid support
Mobile phase: an unreactive gas
To get a well-separated result, start with the column
relatively cool, and then gradually and very regularly
increase the temperature
...


Retention time

The time taken for a component of a mixture to travel
through the column in GLC or HPLC

Factors affecting…
Electron affinities

The charge on the nucleus
...

The distance of the electron from the nucleus
...
An electron
close to the nucleus will be much more strongly attracted
than one further away
...


Rf factor

Attraction between the compound and the solvent
The greater the attraction, the higher the Rf factor
...


Retention time

Boiling point of the compound
A compound which boils at a temperature higher than the
column temperature is going to spend nearly all of its time
condensed as a liquid at the beginning of the column
...

Solubility in the liquid phase
The more soluble a compound is in the liquid phase, the
less time it will spend being carried along by the gas
...

The temperature of the column
The higher the temperature of the column, the higher the
kinetic energy gained by the molecules, the shorter the
retention time
...

- This is because energy is released from the formation of bonds between the ions and
the water molecules
...

- Solubility decreases when going down the group
- Lattice energy and ∆H°hyd become less exothermic when going down the group
- The ∆H°hyd decreases more than the lattice energy
- Enthalpy change of solution becomes less exothermic
Explain the solubility of G2 hydroxides when going down the group
...
g
...

- High resistance to prevent any current flow
What are the functions of the salt bridge and suggest how it can be prepared
...

- CO2 + H2O ⇌ HCO3- + H+
- Excess H+ ions combine with HCO3-
...

- Excess OH- ions are neutralised by H+ ions
...

Why do transition elements often show variable oxidation states in their compound
and not other elements?
- Due to the close similarity of energy of the 4s and 3d sub-shells
Why are complex ions coloured?
- d-orbitals split into 2 different energy levels
- Electrons are excited to higher d-orbitals
- Wavelength is absorbed
- The colour seen is complementary to the light absorbed
Why do different complex ions have different colours?
- Different complex ions have different energy gap / ∆E
- Wavelength absorbed is different
POSSIBLE MECHANISMS
A
...
S2O82- + 2I- → 2SO42- + I2
- S2O82- + I- → SO42- + SO4I- SO4I- + I- → SO42- + I2

Organic Chemistry
Why is chlorobenzene unreactive towards nucleophiles?
- Delocalisation of a lone pair on a Cl atom over the benzene ring strengthens the C-Cl
bond
...
There is an interaction between one
of the lone pairs on the Cl atom and the delocalised electrons, and this strengthens
the bond
...
The OH- will repel
...


Why is phenol a stronger acid than ethanol?
- The electrons on oxygen in phenol are delocalised into the ring
...

- This will lead to the weakening of the O-H bond
...

- It will push its electrons away from itself towards the oxygen atom in the ethoxide ion
...

Why is phenol more reactive than benzene? (the conditions for phenol reactions are
less vigorous than benzene reactions)
- The OH group in phenol is an electron-donating group
...

- The benzene ring in phenol becomes more reactive
...
g
...


Why is carboxylic acid a stronger acid than phenol?
- C=O is an electron-withdrawing group
...

- The COO- is stabilised by the delocalisation of electrons, which spreads out the
negative charge on COO- and reduces its charge density
...

Describe the bonding and structure of benzene
...

- π bonds are delocalised
...

- C-C bonds are of equal length
...

- Bond angles are 120°
...

- π bonding electrons are delocalised
...

- 4 π electrons in the intermediate
...

- π electrons are over the complete ring in benzene
...

- It accepts a pair of electrons from the benzene
...

- H+ on the ring is replaced by NO2+
...

- NO2+ accepts a lone pair
...

Why is benzene less reactive than alkene/cycloalkene?
- Benzene is more stable
...

- Benzene has a lower electron density
...
g
...


Why are halogen carriers good electrophiles?
- Halogen carrier accepts lone pairs of electrons from a halogen atom on an
electrophile
...

Compare the ease of hydrolysis between acyl chlorides, alkyl chlorides and aryl
chlorides
...
(fastest → slowest)
- The C atom of the C-Cl bond in acyl chlorides is more electron-deficient since it is
also attached to the O atom // C-Cl bond is the weakest because it is attached to 2
electronegative atoms
...

- Alkyl chlorides’ C-Cl bond is strengthened by the electron-donating effect of the alkyl
group
...

Compare the boiling points between primary amines with their corresponding alkene
...

Compare the boiling points between secondary amines with their corresponding
primary amines
...

Explain the boiling points and solubility of tertiary amines
...

- However, tertiary amines can form hydrogen bonds with water using the lone pair on
the N atom, making all types of amines soluble in water
...

- Aliphatic primary amines (e
...
methylamine) are stronger bases than NH3
- Methylamine consists of an alkyl group which is an electron-donating group
...

- The methylammonium ion formed is also more stable compared to NH4+ ion because
the positive charge is spread around the ion
...


Compare the basicity of aromatic amines with NH3
...
g
...

- This is because the lone pair on the N atom delocalised into the benzene ring
...

Compare the basicity of amides with NH3
...

- This reduces the availability for the lone pair to bond with H+ ions
...

Why do amino acids have high boiling points?
- When they exist as a zwitterion, they contain positive and negative ions that form a
strong ionic bond with other molecules
...

- Ethylamine > phenylamine > 4-nitrophenylamine (most basic → least basic)
- Basicity is linked to the lone pair on the N atom being able to accept H+ ion
...

- The lone pair on N in phenylamine is delocalised into the benzene ring, reducing its
availability to accept H+ ion
...

Why CDCl3 is used instead of CHCl3 in H1 NMR?
- CDCl3 does not give signal // CHCl3 will give a signal
What happen if D2O is used in H1 NMR?
- OH or NH peak will disappear
- H exchanges with D



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