Chemistry

Reaction kinetics

Reaction kinetics


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Area of ​​Expertise - Physical chemistry

Thermodynamics answers the fundamental question of whether the reaction of educts to the imaginary products is possible at all. In what time this happens, she does not answer. The investigation of the actual time behavior of a chemical reaction is the subject of reaction kinetics.

The reaction kinetics is therefore a branch of physical chemistry. It deals with the reaction rates of chemical reactions.

See also: reaction rate, reaction rate law

Learning units in which the term is dealt with


General

Physical chemistry is a link between chemistry and physics. Here, physical laws are applied to chemical systems.

An example: The description of momentum and energy of moving masses is known from physics (intermediate level material). These laws are used in physical chemistry in the so-called "kinetic impact theory" to describe, for example, the heat conduction or the viscosity ("toughness") of gases. With the help of the kinetic impact theory, in turn, the "reaction kinetics" can be used to describe the speeds of reactions. In physical chemistry, on the one hand, new methods are developed (e.g. lasers and their application in spectroscopy) and, on the other hand, theories are refined (e.g. laws for describing gases).

Examples of typical questions in physical chemistry from everyday life are:

  • Why does a skater slide across the ice? (see phase diagram of water)
  • Why does the "carbonic acid" go out of the hot spring in summer? (see solubility of gases in liquids)
  • How does a laser pointer work? (see spectroscopy.)

Physical chemistry takes on teaching tasks in the subjects Bachelor / Master in chemistry, applied science (Bachelor of Applied Science), food chemistry, and teaching.

The access to Internships, Exercises and lectures do you think ...? Find Left under study documents.


Lithium diisopropylamide: reaction kinetics in solution and implications for organic synthesis

lesson learned: Organic substrates can react with lithium diisopropylamide in a wide variety of ways. The mechanisms of these reactions are complex, but it is still possible to derive simple and practical principles from the experimental results. Particular attention is paid to the influence of solvation and aggregate formation on reactivity.

Abstract

Lithium diisopropylamide (LDA) is an outstanding reagent in organic synthesis. This Review discusses kinetic studies of LDA-mediated reactions, subdividing them into three sections. The first part gives an introduction to the reaction kinetics of LDA solutions with a focus on the characteristic reaction rate behavior, which is determined by solvation and aggregation influences. In the second part, substrate- and solvent-dependent mechanisms are summarized, from which fundamental principles of solvation and aggregate formation can be derived. In the final part, suggestions are made as to how knowledge of the reaction mechanisms can be combined with empirical methods in order to optimize yields, reaction rates and selectivities of organolithium reactions.


Module description

The module BCh 1.1, General and Inorganic Chemistry (Experimental Lecture), represents the basis of chemistry training at the University of Bonn.

Basic chemical principles are taught, e.g. B. the atomic structure according to different models (Dalton, Bohr, quantum mechanical model) and based on this the creation of atomic spectra.

To describe chemical bonds and spatial structures, z. B. Lewis formulas, the MO and valence bond theory and the VSEPR model introduced. Furthermore, the systematics of chemical formula language is conveyed (element symbols, sum formulas) and the implementation of stoichiometric calculations is practiced (setting of reaction equations, substance amount calculations, solubility product, pH value, etc.).

In connection with the term redox reaction, basic electrochemical and thermodynamic terms are discussed (galvanic elements, electrochemical series, Faraday's laws, Hess theorem, reaction kinetics, chemical equilibrium).

In addition to these systematic basics, the characteristic properties and chemical behavior of the main group elements (e.g. alkali and alkaline earth metals, chalcogens, halogens, noble gases) are presented.


Lithium diisopropylamide: reaction kinetics in solution and implications for organic synthesis

lesson learned: Organic substrates can react with lithium diisopropylamide in a wide variety of ways. The mechanisms of these reactions are complex, but it is possible to derive simple and practical principles from the experimental results. Particular attention is paid to the influence of solvation and aggregate formation on reactivity.

Abstract

Lithium diisopropylamide (LDA) is an outstanding reagent in organic synthesis. This Review discusses kinetic studies of LDA-mediated reactions, dividing them into three sections. The first part gives an introduction to the reaction kinetics of LDA solutions with a focus on the characteristic reaction rate behavior, which is determined by solvation and aggregation influences. In the second part, substrate- and solvent-dependent mechanisms are summarized, from which fundamental principles of solvation and aggregate formation can be derived. In the final part, suggestions are made on how knowledge of the reaction mechanisms can be combined with empirical methods in order to optimize yields, reaction rates and selectivities of organolithium reactions.


General

The aim of the bachelor's degree is to acquire a solid basic education in chemistry. The students are given the necessary technical knowledge and skills, they are instructed to think independently and to act independently. A broad-based academic degree is intended to open up professional fields of activity in industry, business and administration.

Chemistry is predominantly an experimental natural science. Chemists deal with the manufacture and properties of substances. Traditionally, a distinction is made between three main areas: The Organic chemistry (Chemistry of the carbon compounds from which e.g. all living organisms are built) that Inorganic chemistry (Chemistry of the other elements and their compounds) and the Physical chemistry (Experimental investigations of material properties, laws, theoretical chemistry, development of theoretical systems, models and methods). Special areas are also analytical chemistry, macromolecular chemistry, technical chemistry, radiochemistry and biochemistry.

In chemistry studies, alongside the acquisition of knowledge, which, in view of the growing amount of scientific knowledge, can only be acquired by way of example, is the Mastery of experimental and theoretical methods in the foreground, which deal with chemical reactions (material conversions) and structural clarifications. The acquisition of "object-related" knowledge and skills is of great importance in the context of chemistry studies. In addition to the theoretical courses (lectures, seminars, exercises) there are therefore the Internships in the foreground - they take up about half of the entire study time.

The boundaries between the neighboring natural sciences and technical disciplines are fluid; this applies in particular to mathematics, physics, biology, mineralogy, pharmacy and process engineering. Chemistry students should therefore not only enjoy experimenting and be able to critically observe, but also have an interest in and understanding of other subject areas.
Much of the chemical scientific literature appears in English. Knowledge of English is therefore essential for the chemist and should be acquired during the course of the bachelor's degree at the latest.

The standard period of study is including the examination times six semesters. The bachelor's degree has a modular structure and comprises the specialist studies and overarching competencies.


Interpretation of the Gibbs-Helmholtz equation $ Delta G = Delta H - T cdot Delta S $

Thermodynamics of the chemical reaction

The driving force for a chemical reaction to take place is the increase in entropy S in the universe (see. 2nd law of thermodynamics).

If one considers a system that cannot exchange heat with the environment (adiabatic system), the only condition that has to be placed on a spontaneously occurring process is $ Delta S_ < rm System> & gt 0 $. The decisive factor here is not whether the individual reaction is exergonic or endergonic, but rather that the system is not yet in equilibrium.

Exothermic and endothermic reaction

If the system is allowed to exchange heat with the environment (diabatic system), the change in entropy in the environment must also be taken into account. This can be recorded via the enthalpy change in the system $ mathrm < Delta H> $:

  • as a negative contribution if the reaction is exothermic, thermal energy is distributed to the environment and in this way the entropy increases in the environment,
  • as a positive contribution if the reaction is endothermic and the entropy in the environment decreases because thermal energy is concentrated in the reaction vessel.

The system strives for states with minimal free enthalpy G because this is the state of maximum entropy.


2. CV

ERWIN SCHRÖDINGER was born on August 12th. Born in Vienna in 1887.
Here he attended high school, graduated from high school and began to study.
The most important teacher for ERWIN SCHRÖDINGER was FRIEDRICH HASENÖHRL. The student studied theoretical physics with him for eight semesters (five hours per week each).

SCHRÖDINGER received his doctorate in Vienna in 1910.
He then worked as an assistant at FRANZ EXNER at the Second Physics Institute at the University of Vienna.
From 1920 onwards, SCHRÖDINGER's “years of travel” began.
The young scientist first went to Germany as a lecturer for a semester, to Jena, and then to Stuttgart.
In 1921 he moved to Breslau as a full professor. In the same year ERWIN SCHRÖDINGER was appointed to the University of Zurich. He then stayed in Switzerland for six years.

During these years he was preoccupied with numerous scientific problems. SCHRÖDINGER was particularly fond of statistical heat theory. Investigations into gas and reaction kinetics, lattice vibrations and their contribution to the internal energy of a system formed the basis of his research.
In addition, the scientist dealt with the methods of mathematical statistics.
His publications on the theory of specific heat and statistical thermodynamics summarized the findings. During this time, SCHRÖDINGER also worked closely with other scientists, e. B. with PETER DEBYE and with HERMANN WEYL.

At the same time, SCHRÖDINGER dealt with NIELS BOHR's ​​quantum theory and ALBERT EINSTEIN's theory of relativity.
He was also less interested in physics-theoretical topics. So he explored the theory of color vision and carried out measurements and calculations on the metrics of color space. As a result, he published his findings, which are still true today, on the frequency of red-green blindness and blue-yellow failure.

In 1924 LOUIS DE BROGLIE's doctoral thesis was published, with which the idea of ​​wave-particle dualism was born.
This work and the discoveries of NIELS BOHR, e.g. B. Bohr's atomic model (1913) and its extension, the BOHR-SOMMERFELD atomic model (1921), formed the basis for further discoveries by SCHRÖDINGER. ALBERT EINSTEN's work also played an important role in this.

SCHRÖDINGER first applied his findings to gas theory in order to then transfer it to individual atoms. He intensified his research when he noticed that he had come across a "new atomic theory".
In 1925, SCHRÖDINGER wrote to WILHELM WIEN, the editor of the Annalen der Physik:
“At the moment I am plagued by a new atomic theory. If only I could do more math! I am very optimistic about this and hope that if I can only do it arithmetically, it will be very nice. "

In 1926 the time had come, the basic features of wave mechanics could be published. His New quantum theory was initially judged derogatory by the specialist colleagues, especially the Göttingen district. Only when he succeeded in demonstrating the “identity” of matrix and wave mechanics in formal mathematical terms did they have to accept his findings.
In his first publications, SCHRÖDINGER spoke of the wave function (F) as an oscillation amplitude in three-dimensional space and thus of something that was immediately clear.
He then tried to interpret the quantity F as an electrical charge density in order to help physics to come up with a uniform wave concept. In the first approach he assumed that the charge of an electron was a standing wave distributed around the nucleus, analogous to the vibration of a stretched string or standing waves on limited surfaces
In contrast to this idea, however, the experiments showed strictly localized particles. Therefore, SCHRÖDINGER tried to introduce the concept of the wave group, unfortunately with moderate success. With this, too, the particle character could not be fully captured.

In 1927 SCHRÖDINGER was appointed from Zurich to Berlin, where he taught and researched at the university as MAX PLANCK's successor until 1933.
As early as 1933, he and DIRAC received the Nobel Prize for Physics for their knowledge of quantum mechanics (SCHRÖDINGER equation)
The SCHRÖDINGER equation is the fundamental equation of motion for atomic particles.

ERWIN SCHRÖDINGER was a staunch liberal all his life and so he left Germany in 1933 after the Nazis came to power.
He first went to Oxford for two years, then moved to Graz in 1936 and finally to Ghent in 1938.
In Dublin in 1940 the physicist first took up a position as professor at the “Royal Irish Academy” and soon afterwards founded the “Institute for Advanced Studies”. The institute granted generous scholarships to young scientists, especially from the field of physics, and so numerous researchers gathered at the SCHRÖDINGER institute.

The annual “Summer School”, an informal meeting where current questions in physics were discussed, soon became famous.
In Dublin, ERWIN SCHRÖDINGER continued to work on wave mechanics. He published numerous publications, e.g. B. on the application and statistical interpretation of wave mechanics, on the mathematical character of the new statistics and the relationship to statistical heat theory.

He was also concerned with questions of relativity, especially the relativistic treatment of wave fields in contrast to the initially nonrelativistically formulated wave mechanics.
However, SCHRÖDINGER's special research interest remained the further development of EINSTEIN's theory of gravity , especially the interaction forces between particles.

It was not until 1956 that ERWIN SCHRÖDINGER returned to his home country Austria, to the university in Vienna, where he was still active for two years. In recent years the physicist has dealt in depth with the fundamentals of physics and their significance for worldview and philosophy. He published several studies on it in English at Cambridge University Press, which he also translated himself.

In 1958 ERWIN SCHRÖDINGER retired and spent the last few years in the midst of the Tyrolean mountains he loved, in Alpbach.
He died on January 4th, 1961 in Alpbach.


Video: Class 12 chap 3: Chemical Kinetics 01: Introduction - Rate of Reaction JEE MAINSNEET (May 2022).