CHEMICAL KINETICS WITH LABORATORY
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- Versione italiana
- Academic year
- 2022/2023
- Teacher
- ROBERTO ARGAZZI
- Credits
- 8
- Didactic period
- Primo Semestre
- SSD
- CHIM/02
Training objectives
- Knowledge and Understanding
The Chemical Kinetics and Laboratory course gives basic and advanced knowledge for a full understanding of the phenomena determining the temporal evolution of physico-chemical systems, completing the background acquired in other Chemistry and Physics courses. Fundamental notions and kinetic laws governing chemical transformations and transport phenomena are provided allowing the student to understand in depth and to interpret reaction mechanisms.
Knowledge and Understanding application.
At the end of the course, the student is able to critically apply the knowledge acquired on the reaction kinetics and on transport phenomena leading to a full theoretical interpretation of the mechanisms of the observed physico-chemical processes and to the practical application of the related experimental techniques. He is also able to transfer this knowledge to the description of real systems. Prerequisites
- The course “Chemical Kinetics and Laboratory” requires a firmly founded knowledge of Physics and Maths (complete programs of the courses for chemists) and a good background of Chemical Thermodynamics, as supplied by the attendance of the Physical Chemistry I course. I.
Course programme
- Kinetic view of thermodynamic equilibrium: elementary reactions and rate laws, example of the reaction between gaseous hydrogen and bromine. The need for a reaction mechanism hypothesis. Extent of reaction and reaction rate definition. Volume change in isothermal systems. Rate laws in diffferential form. Molecularity and global and partial reaction orders. Zero order reactions. Elementary reactions of order one, two and n. Integrated laws. Lifetime and half life. Kinetic schemes composed of several elementary steps: opposed reactions, parallel reactions and consecutive reactions. Quasi steady state approximation and its validity limit. Consecutive reactions with pre-equilibrium: approximate solution and kinetic regimes. The Lindemann-Hinshelwood mechanism for unimolecular gas phase reactions. Experimental determination of rate laws and reaction orders: isolation and initial rate methods. Influence of temperature on reaction rate. Empirical Arrhenius law. Activation energy and its experimental determination. Radical reactions. Christiansen-Herzfeld-Polanyi mechanism. Branched chain reactions: explosive limits. Polymerization reactions: step-growth and chain mechanisms. Radiation-matter equilibrium: elementary processes and Einstein’s coefficients. Photon flux and complete continuity equation. Spatial variation of photon flux density in a homogeneous medium: attenuation (Beer-Lambert law) and amplification (Laser). Photochemical Kinetics. Excited state unimolecular processes: lifetime and quantum efficiencies. Stationary solutions. Kinetics of singlet-triplet transitions. Excited state bimolecular processes: dynamic and static quenching. Stern-Volmer relation. Stationary and pulse excitations. Kinetic theory of the perfect gas. Maxwell-Boltzmann distribution law: properties and average values calculation. Kinetic energy distribution and equipartition principle. Flux density vector for gas particles in thermal equilibrium. Average scalar flux density calculation. Knudsen effusion method for vapour pressure determination. Kinetic calculation of the pressure exerted by a gas: Clausius-Kronig equation and derivation of the perfect gas state equation. Reactive collision theory: relative velocity, collision parameter and collision cross-section. Frequency and density of collisions. Mean free path. Effective collision criterion and threshold energy. Calculation of the kinetic constant for a bimolecular gas phase reaction. Steric factor correction. Microscopic theory of transport processes in a thermally equilibrated gas. Calculation of the average value of the mean free path projected along a direction. Scalar flux density of a transported property in the presence of a uniform gradient: heat flow (Fourier’s law), mass flow (Fick’s law), momentum flow (Newton’s law). Charge transport in an electrolytic solution under an electric field. Drift velocity and ionic mobility. Current density and molar conductivity. Kohlrausch’s limit law. Ostwald’s dilution law. Chemical potential gradient as a thermodynamic force and its related diffusion flux. Einstein, Einstein-Stokes and Einstein-Nernst relations. Fick’s second law and its solution for the thin film unidimensional case. Einstein-Smoluchowski relation. Diffusion in three dimensions indipendent from direction. General transport equation including diffusion and convection. Diffusion controlled reactions: Smoluchowski’s theory. Eyring’s transition state theory. Thermodynamic considerations on Eyring’s equation. Effect of ionic strength on the rate of a reaction involving ionic species. Charge transfer reactions in solution: Marcus’ model. Reorganization energy and inverted region. Charge transfer at the electrode solution interface: Butler-Volmer’s equation. Tafel’s plot. Homogeneous catalysis: acid-base and enzimatic. Michaelis-Menten’s mechanism. Lineweaver-Burk’s plot. Competitive and non competitive inhibition. Heterogeneous catalysis. Physical and Chemical adsorption. Langmuir’s adsorption model. Isosteric enthalpy. Reactions on solid surfaces: Langmuir-Hinshelwood’s mechanism. Experimental techniques for the study of fast reactions. Flow and stopped-flow methods. Relaxation methods: pressure jump, temperature jump and flash photolysis. Pump-probe ultrafast laser spectroscopy.
Didactic methods
- The course is based on theoretical lessons and on four laboratory experiences suitably illustrated in detail before the start of the experimental activities. For the practical laboratory activity, students will be associated in working groups and the number of members of each group will be decided on the basis of the total number of participants. Each group will be asked to write a report for each of the experiences carried out.
Learning assessment procedures
- The exam is oral. The candidate will be asked three questions, the first of which is on a topic of his or her choice. Each question will be awarded a maximum score of four points. The exam can be divided into two partial tests and the final grade will result from the arithmetic average of the two assessments.
Reference texts
- 1) P. W. Atkins, J. De Paula, J. Keeler - "Chimica Fisica", 6a edizione (2020), Zanichelli, BO.
2) P. L. Houston - "Chemical Kinetics and Reaction Dynamics", (2001), Dover Publications, Inc., Mineola, New York.
