Energy Profile Diagram and Stability

Aashutosh Anand Semester 1

1. SAMRAT PRITHVIRAJ CHAUHAN GOVERMENT COLLEGE,AJMER M.Sc. Chemistry Semester - 1 PRESENTED BY – AASHUTOSH ANAND

2. Key-Points Introducation of Energy Diagram Energy profile Diagram i n Chemistry Types of Energy/Reaction Difference between S N 1 and S N 2 Reactions Genral Model of Energy Diagram EPD for S N 2 Reaction Difference in Exo and Endo thermic Reaction Different types of S N 2 Reaction EPD for S N 1 Reaction Stability of Complexes Types of stability of complexes Stable and Unstable complex Kinetic stability Inert and labile complex Factors affecting stability of Metal complex Refrences

3. Introduction of Energy Diagram 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. Energy Profile Diagram In Chemistry 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 S N 1 and S N 2 both type according to their conditions EPD for the same reaction is diffrent , It means EDP is depend on Reaction mechanism

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

6. Difference between S N 1 and S N 2 Reaction S N 1 Reaction Unimolecular Nucleophilic Substitution Reaction Occurs in 2 steps Produce s a carbocation as an intermediate Reaction Mechanism- S N 2 Reaction Bimolecular Nucleophilic Substitution Reaction Occurs in 1 steps No intermediate is produced Reaction Mechanism-

7. Genral Model of Energy Diagram

8. EPD for S N 2 Reaction ENERGY DIARGRAM- This reaction occurs in single step so One transition state is formed It may be exothermic or endothermic reaction

9. Difference in Exo & Endo thermic Rxn 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

10. Different type of S N 2 Reaction

11. EPD FOR S N 1 Reaction 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. Stability of Complexes 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(NH 3 ) 4 ]SO 4 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. Type of Stability of complexes We can diffrentiate the stability of complexes on the basis of: Thermodynamic stability 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- Stable complex Unstable complex

14. Stable and Unstable complex 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. 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. Kinetic stability 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 . Inert complex Labile complex According to Taube 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. Inert and labile complex (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. Factors affecting Stability of Metal Complexes 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- Factors pertaining to metal Factors pertaining to ligand Solvent effect

18. Factors pertaining to metal-Ion 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. M 2+ Mn 2+ Fe 2+ Co 2+ Ni 2+ Cu 2+ Zn 2+ < < < < > 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 M 2 + Be 2 + > Mg 2 + > Ca 2 + > Sr 2 + > Ba 2 + 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 . M n + La 3+ > Sr 2+ > K + r( Å) 1.12 1.13 1.33 Similary M n + Th 3+ > Y 3+ > Ca 2 + > Na + r( Å) 0.95 0.93 1.14 1.16

21. Factors pertaining to ligand - The following properties of ligands attached affect the stability of the transition metal complexes to a significant extent. 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 NH 3 should be a better ligand than H₂O which in turn should form more stable complexes than HF . NH 3 > H₂ O > HF For Group-A Metal For Group-B Metal F - > Cl - > Br - > I - F -   < Cl -   < Br -   < I -

23. Refrence : Stability in complexes By J.E. Huheey Inorganic Chemistry B.Sc part 2 nd By G.K. Rastogi and Dr. Yashpal singh

24. Thank-You