CHEMISTRY

9701
A2

WELCOME
TO
SESSION 2025-26

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 • Thermodynamics • Transition Elements
• Equilibria
• Kinetics
• Electrochemistry

Physical Inorganic
A2 SYLLABUS Chemistry Chemistry
CONTENT

Organic Analytical
Chemistry Chemistry
•Arenes
•Phenols
•Acyl Chloride • Chromatography
•Nitrogen Compounds
•Polymerization • NMR Spectroscopy
•Drug Synthesis
 Expectations
What should a good Chemistry classroom look like?

• Consistency: attendance, punctuality, and participation

• Preparation: bring textbooks, calculator, and notes

• Practice: complete assigned work and past papers on time

• Engagement: ask questions, share ideas, and collaborate

 Energy level diagrams
28/08/2025

Energy
level

Activation
energy

Energy given
out by
Using a catalyst reaction
might lower the
activation energy

Reaction progress
 1 Pic 1 Sentence
28/08/2025

Very endothermic reaction with a big activation

energy.

Very exothermic reaction with a small activation

energy.

Moderately endothermic reaction with moderately

high activation energy.

Moderately exothermic reaction with a

moderately high activation energy.
 28/08/2025

A small activation energy reaction with

no net energy change. (Possible if the total energy
absorbed by the reactants in bond breaking equals the energy
released by bonds forming in the products)

Energy level diagram for an endothermic

chemical reaction without showing the
activation energy.
DISCUSS AND DEFINE THE FOLLOWING TERM

First
Ionization
energy
SECOND IONIZATION ENERGY
Second ionization energy is the energy required to remove the one mole of the
electron from one mole of gaseous +1 ion to form one of gaseous (+2) charged
ion, under standard conditions

Na+2 (g) → Na+2 (g) + e- ∆Hᶲi.e2 = +ve

Ionization energy increases with the removal of each electron. Each time an electron is
removed, the effective nuclear charge increases, causing the remaining electrons to be
held more tightly and making the radius smaller.
 ELECTRON AFFINITY

 Energy change when an electron is added to a gaseous atom or ion in the

ground state:

X(g) + 1e- → X-(g)

usually exothermic process

.
 ELECTRON AFFINITY
 Energy change when an electron is added to a gaseous atom or ion in the ground state:

X(g) + 1e- → X-(g)

usually exothermic process

If removing an electron is endothermic, then the reversed process is exothermic .
An isolated electron is brought from far away to undergo attraction to the nucleus
which lowers its energy → Excess energy released.

7e-
2e-
e- 9
+

F(g) + 1e- → F-(g) H=-328 kJ/mol

  First electron affinity, ∆Hᶲe.a1, is the enthalpy
change when one mole of the electron is
added to one mole of gaseous atoms to form
one mole of gaseous (1-) ion, under standard
conditions

FIRST ELECTRON  Cl(g) + e- → Cl-1 (g) ∆Hᶲe.a1 = -ve

AFFINITY
S(g) + e- → S-1 (g) ∆Hᶲe.a1 = -ve

It is always exothermic, ∆Hᶲe.a1 = -ve, because

energy is released when an electron is gained.
  Second electron affinity, ∆Hᶲe.a2, is the enthalpy
change when one mole of the electron is added
to one mole of gaseous (1-) ion to form one
mole of gaseous (2-) ion, under standard
SECOND conditions.
ELECTRON  S-1(g) + e- → S-2 (g) ∆Hᶲe.a2 = +ve
AFFINITY,

It is always endothermic, ∆Hᶲe.a1 = +ve because

energy is needed to overcome the repulsive forces
between electrons and negatively charged ions.
 More Negative
PERIODIC TRENDS
IN ELECTRON
AFFINITY

More Negative
 The more negative electron
affinity means greater
energy is released means
greater nuclear attraction
towards the added electron.
EXPLAIN THE
TREND DOWN
GROUP 16 AND
17
  In Group 16, 17 electron affinity
becomes less negative because of the
EXPLAIN THE decreased attractive force from the
TREND DOWN
GROUP 16 AND nucleus as shielding by inner
17 electron shells increases down the
group.
DISCUSS AND DEFINE THE FOLLOWING TERMS

Enthalpy Enthalpy
Change of Change of
Atomization Formation
ENTHALPY CHANGE OF ATOMIZATION

 It is the enthalpy change when one mole of gaseous

atoms is formed from its element under a standard
state.
 It is denoted by
 For e.g., Na (s) Na(g)
ENTHALPY CHANGE OF ATOMIZATION

Write the equation to show the atomization of

1. Lithium
2. Chlorine
3. Bromine
4. Neon
ENTHALPY CHANGE OF ATOMIZATION
ENTHALPY CHANGE OF FORMATION
Definition The enthalpy changes when ONE MOLE of a substanceis formed from its elements
under standard states.

Symbol  f or Hf

Values Usually, but not exclusively, exothermic

Example(s) C(graphite) + O2(g) ———> CO2(g)

H2(g) + ½O2(g) ———> H2O(l)

2C(graphite) + ½O2(g) + 3H2(g) ———> C2H5OH(l)

Notes Only ONE MOLE of product on the RHS of the equation

Elements In their standard states have zero enthalpy of formation.
Carbon is usually taken as the graphite allotrope.
DEFINE THE FOLLOWING TERM

Hess’s Law
 Hess’s law states that ‘the total enthalpy change in a
chemical reaction is independent of the route by
which the chemical reaction takes place as long as
the initial and final conditions are the same’.

HESS’S LAW
LATTICE
ENERGY
STANDARD LATTICE ENTHALPY
Standard Lattice Enthalpy, ∆Hᶲlat

The enthalpy change when ONE MOLE of an ionic lattice is formed from its isolated gaseous
ions, under standard conditions ( 1 atm, 298 K)

Values highly EXOTHERMIC

strong electrostatic attraction between oppositely charged ions
a lot of energy is released as the bond is formed
relative values are governed by the charge density of the ions.

Example Na+(g) + Cl¯(g) Na+ Cl¯(s)

Na+(g) + Cl–(g)

∆Hᶲlat
NaCl(s)
LET’S APPLY THE KNOWLEDGE

 Sodium metal reacts with chlorine gas to form sodium chloride, NaCl.
Write an equation, including state symbols, to represent the lattice energy of
sodium chloride.
LET’S APPLY HESS’S LAW TO MAKE THE ENTHALPY CYCLE FOR
CALCULATING THE LATTICE ENTHALPY OF SODIUM CHLORIDE
CALCULATING LATTICE ENTHALPY

 We cannot calculate the lattice enthalpy directly as

it is the energy released when one mole of an ionic lattice is formed from its
isolated gaseous ions.
 However, we can experimentally determine the enthalpy change of formation and
then make an enthalpy cycle using Hess’s law.
  First draw a vertical line to represent the y-axis, which will be the
enthalpy scale
 Then draw a horizontal line to represent the x-axis and put the
ionic solid on this line

DRAWING BORN-  A line is then drawn at the top to represent the highest energy
point (optional)
HABER CYCLES  Next, the elements needed to form the ionic solid are placed in
their standard states on a line above the ionic solid
 This line corresponds to zero energy

 Continue to add the other steps until you end up with the gaseous
ions needed to form the ionic solid
+e
BORN HABER
CYCLE
BORN HABER CYCLE FOR

2. Na2O
Use the information below to calculate the lattice enthalpy and draw
Born–Haber Cycle for CsF(s)
Reaction Enthalpy Change (kJ/mol)

(1) Cs(s) → Cs(g) ΔHatm (Cs) = 76.5

(2) Cs(g) → Cs + (g) + e− ΔHi1 = 375.7

(3) ½F2(g) → F(g) ΔHatm (F) = 79.4

(4) F(g) + e− → F−(g) ΔHea1 = −328.2

(5) Cs(s) + ½F2(g) → CsF(s) ΔHf = −553.5

FACTORS AFFECTING LATTICE ENTHALPY

Lattice Enthalpy Values

Cl¯ Br¯ I¯
Na+ -787 -751 -705
K+ -711 -679 -632 Units: kJ mol-1

Compare the Lattice Enthalpies of NaCl, NaBr, and NaI.

Q1. Do you observe any trend?
Q2. Explain your observation
FACTORS
AFFECTING THE
LATTICE ENTHALPY

smaller the ionic radius,

shorter the distance,

stronger the electrostatic

attraction
FACTORS AFFECTING LATTICE ENTHALPY

Lattice Enthalpy Values

Cl¯
Na+ -780
Mg2+ -2256

Units: kJ mol-1

Compare the Lattice Enthalpies of NaCl, and MgCl 2..

Q1. Do you observe any trend?
Q2. Explain your observation
 Factors • The greater the charge of the ions,
the stronger the electrostatic
affecting the attraction
lattice enthalpy
FACTORS AFFECTING THE LATTICE ENTHALPY

Newton's law of universal gravitation

says that every particle attracts every
other particle in the universe with a
force that is proportional to the product
of their masses and inversely
proportional to the square of the
distance between their centers.
FACTORS AFFECTING THE LATTICE ENTHALPY
EXAMPLE 1
⚫ high charge F– O2– N3–

increasing lattice enthalpy

⚫ small size. K+ Na+ Li+

Question Time
TRY IT
YOURSELF !
 Summary

greater charge
densities of ions = greater attraction
= larger lattice enthalpy

you CAN NOT MEASURE LATTICE ENTHALPY DIRECTLY

it is CALCULATED USING ENTHALPY CYCLE

Effects

Melting point the higher the lattice enthalpy,

the higher the melting point of an ionic compound

Solubility solubility of ionic compounds is affected by the relative

values of Lattice and Hydration Enthalpies