This document discusses energy diagrams and types of stability in chemistry. It begins with an introduction to energy diagrams and how they are used to represent energy changes during chemical reactions. It then discusses different types of reactions like SN1 and SN2 and how their energy profiles differ based on reaction mechanism. It also defines terms like activation energy, reaction energy, exothermic and endothermic reactions. The document goes on to explain kinetic and thermodynamic stability of complexes and factors that influence the stability of metal complexes like size and charge of the metal ion, basicity of ligands, and solvent effects.

1. (1) ENERGY PROFILE DIAGRAM
(2)TYPES OF STABILITY
M.Sc. Chemistry Semester - 1
PRESENTED BY – AASHUTOSH ANAND

2. 1. Introducation of Energy Diagram
2. Energy profile Diagram in Chemistry
3. Types of Energy/Reaction
4. Difference between SN1 and SN2 Reactions
5. Genral Model of Energy Diagram
6. EPD for SN2 Reaction
7. Difference in Exo and Endo thermic Reaction
8. Different types of SN2 Reaction
9. EPD for SN1 Reaction
10. Stability of Complexes
11. Types of stability of complexes
12. Stable and Unstable complex
13. Kinetic stability
14. Inert and labile complex
15. Factors affecting stability of Metal complex
16. Refrences

3. • Energy Diagram - A Diagram/Graph that represents the flow
of energy with time or stage
Energy Diagram is used in Science at diffrent places like-
Biology - Lindeman 10% Rule
Ecology – Food chain
Chemistry – Reaction Profile
Etc ...................

4.  Diagram tha represents energy change during a Chemical Reaction
Let us consider the following Reaction-
X +Y-Z X-Y + Z
 Same Reaction happen in SN1 and SN2 both type according to their conditions
EPD for the same reaction is diffrent, It means EDP is depend on Reaction
mechanism

5. Activation
Energy
Reaction
Energy
Types of
Energy
Exothermic
Endothermic
Type of
Reaction
Before we learn how to draw EDP for an reaction lets familier with these
terms

6.  SN1 Reaction
1. Unimolecular Nucleophilic
Substitution Reaction
2. Occurs in 2 steps
3. Produce s a carbocation as an
intermediate
Reaction Mechanism-
 SN2 Reaction
1. Bimolecular Nucleophilic
Substitution Reaction
2. Occurs in 1 steps
3. No intermediate is produced
Reaction Mechanism-

8. ENERGY DIARGRAM-
This reaction occurs in single step so One transition state is formed
It may be exothermic or endothermic reaction

9. EXOTHERMIC REACTION
 Energy is given out to the
surroundings.
 Heat of reaction is
negative.
 Products have less energy
than reactants.
 Exo means Release
 Ex- Respiration, Fireplace,
Combustion
ENDOTHERMIC REACTION
 Energy is taken in from the
surroundings
 Heat of reaction is
positive
 Products have more energy
than reactants
 Endo means Absorb
 Ex- Photosynthesis

11. Energy Diagram:
This reaction occurs in two steps so two transition states is form
In this reaction a carbocation is formed which works like an intermediate

12. If we say this complex is stable or not , our means is to how much time we can
store that complex in nature and this complex doesnot oxidise or reduct.
But it is ready to acknowledge one complex which is stable for some condition
It may be unstable for another condition
For example: [Cu(NH3)4]SO4
is an stable substance, we can store for a long time in
in solid state but when we put it in acidic aquous solution this substract is
reduct in very short period of time.

13. We can diffrentiate the stability of complexes on the basis of:
1. Thermodynamic stability
2. Kinetic stability
Thermodynamic Stability:
This is a measure of the extet to which the xomplex will form or will be
transformed into another species.When the system has reached equilibrium
This stability deals with the properties like bond energies, stability constants and
redox potential that affect the equilibrium conditions.
On the basis of thermodynamic stability of complex in solution,
Biltz(1927) has classified complex in the following types-
a) Stable complex
b) Unstable complex

14. A. Stable (Penetration) complex:
 Stable complexes are those which possess sufficient stability to retain their
identity in solution.
 Thermodynamically stable complex has high value of formation constant.
B. Unstable (Normal) complex:
 Unstable complexs are those which are reversibly dissociated in solution into
their components.
 Thermodynamically unstable complex has low value of formation constant.
Stability of complex depends on there bond strength
For example-
Co(SCN)2 the bond strength between Co-S is weak so this complex is
thermodynamically unstable
Fe(CN)2 bond strength between Fe-CN is strong so this complex is
thermodynamically stable

15.  It deals with speed of transformation leading to attainment of equilibrium.
 This kind of stability deals with role of reaction, mechanism or reaction, formation
of intermediate activation energy of the process.
On the basis of rate of reaction (i.e. kinetic sability) of the complex in solution
Taube(1950) classified complex into two types .
1. Inert complex
2. Labile complex
According toTaube in substitution reaction if reaction in completed in less than
1 min at room tempreture and 0.1 M solution is taken than the complex is called
labile

16. (1) Labile complex:
 Labile complex are those whose one or more ligands in the oordinatio sphere can
be rapidly replaced by other ligands.
 The ability of a complx to replace its one or more ligands by other lignads is called
its lability
 Labile complex is also called Kinetically labile.
(2) Inert complex:
 Inert complexes are those whose one or more lignads can either not be replaced or
can be replaced with difficulty by other ligands.
 Inert complex is also called Kinetically inert.
There is no correlation between thermodynamic and kinetic staility
i.e.
Thermodynamic stable- may be labile or inert
Thermodynamic unstable – may be labile or inert

17. The stability of metal complexes depends upon a number of factors but it largely
governed by the nature and the coordinative environment of the ligands attached
and the nature of the central metal ion or atom itself.
We learn affecting factors with 2 type-
1) Factors pertaining to metal
2) Factors pertaining to ligand
3) Solvent effect

18. 1) Size of the cation- The stability of metal complexes decreasees
with the increase in size of central metal ion provided the valency
and ligands the same.
Thus , the stability of isovalent complexes decreases down the
group and increases along the period as the size varies in the
reverse order.
Example- Stability order of hydroide compleses of alkali metal ions and
alkaline earth metal ions is:

19. Stability order of metal complexes formed by bivalent metal ions of the first
transition series, which is known as Irving-William series are given below.
M2+ Mn2+ Fe2+ Co2+ Ni2+ Cu2+ Zn2+
< < < < >
r(Å) 0.91 0.83 0.81 0.78 0.69 0.74
M+ Li+ > Na+ > K+ > Rb+ > Cs+
r(Å) 0.60 0.95 1.33 1.48 1.95
similarly
M2+ Be2+ > Mg2+ > Ca2+ > Sr2+ > Ba2+
r(Å) 0.31 0.65 0.99 1.33 1.35

20. 2)Charge On Central Metal Ion- The stability of transitin metal
complexes with the same ligands and similar coordinative environment,
increase with the increase of the charge on the central metal aton or ion.
Therefore, the greater is the charge on the central ion, the higher will be the
stability of the metal complexe.
Mn+ La3+ > Sr2+ > K+
r(Å) 1.12 1.13 1.33
Similary
Mn+ Th3+ > Y3+ > Ca2+ > Na+
r(Å) 0.95 0.93 1.14 1.16

21. The following properties of ligands attached affect the stability of the transition
metal complexes to a significant extent.
1) Charge and Size of ligand: Just like the metal, the charge and
size of the ligand also play a significant role in deciding the stability of
the transition metal complexes.
Smaller size ligands are expected to form more stable complexes as
they can approach the metal ion more closely and ligands with higher
charges. But this is only true for the Group A metal ions.
But the case is reversed in the case of Group B metal ions.
Group A Metal – Alkali metal and alkaline earth Mertal
Group B Metal- D block metal

22. 2) Basicity of the ligand-
 Stability of the metal complexes increase with the increase in the
basic nature of the ligands as the donation of electron pair
becomes more favorable.
 Thus NH3 should be a better ligand than H₂O which in turn should
form more stable complexes than HF.
NH3 > H₂O > HF
For Group-A Metal
For Group-B Metal
F- > Cl- > Br- > I-
F- < Cl- < Br- < I-

23.  Stability in complexes
By J.E. Huheey
 InorganicChemistry B.Sc part 2nd
By G.K. Rastogi and Dr.Yashpal singh

24. Thank-You