Physical chemistry
The physical chemistry (in short: PC) is in addition to the inorganic and organic chemistry, one of the " classical" branches of chemistry. It deals with the interface between physics and chemistry, in particular the application of the methods of physics to objects of chemistry. While in the preparative chemistry are questions of methodology for chemical synthesis of known and new substances in the foreground, the physical chemistry tries to describe the properties of materials and their conversion with the help of theoretical and experimental methods, with the aim for all relevant processes generally valid mathematical establish formulas with clearly defined units and the exact numerical values.
Naturally, there is a great closeness to physics ( in particular for molecular physics ), and the classification of a research topic as " physics " or " chemistry" is often not very clear. Nevertheless, partially differentiated, depending on the focus between physical chemistry and chemical physics. Physical chemistry provides the theoretical basis for the Chemical Technology and process engineering. Chemists, who are mainly active in the field of physical chemistry are referred to as a physical chemist. Physical chemistry is a must part of any study of chemistry.
- 4.1 General Textbooks
- 4.2 Physico-chemical journals
History
The physical chemistry was in 1890 by Svante Arrhenius, Jacobus Henricus van ' t Hoff, Wilhelm Ostwald and Walther Nernst introduced as a separate school subject at universities. Previously, there was already a scientist who dealt with physico-chemical problems (eg Thomas Graham, Joseph Louis Gay -Lussac, Robert Wilhelm Bunsen, Hermann Helmholtz, Robert Boyle etc. ), an independent school subject was physical chemistry at universities However, it is not. In the Anglo -Saxon Josiah Willard Gibbs regarded as the founder of physical chemistry with his 1867 article, " On the Equilibrium of Heterogeneous Substances ", in which he developed the basic concepts of free energy, chemical potential and phase rule. The work of Gibbs, Robert Mayer, Hermann Helmholtz, Jacobus Henricus van ' t Hoff made for Wilhelm Ostwald an important concatenation of the energy concept a chemical perspective.
Gustav Wiedemann received in 1871 in Leipzig Germany's first professorship in physical chemistry was not until 1887 could by replacement of the Department manifest with Wilhelm Ostwald physical chemistry research. Ostwald was the first editor of 1887, together with van ' t Hoff founded journal of physical chemistry, stoichiometry and affinity teaching. More specifically physical chemistry devoted Institute then followed the suggestion of his student Walther Nernst in rapid succession in Göttingen ( 1891), Dresden ( 1900), Karlsruhe (1900 ), Berlin ( 1905), Aachen ( 1906), Breslau (1910 ) and elsewhere.
Wilhelm Ostwald founded in 1894 the German Electrochemical Society, which was renamed in 1901 German Bunsen Society for Applied Physical Chemistry. In England, the Faraday Society ( Faraday Division today the Royal Society of Chemistry ) was established in 1903. Meanwhile, countless university and several Max Planck Institutes deal with physical chemistry.
A detailed overview of the emergence and development of physical chemistry is a review article of the Bunsen Society More details can be found at History of Chemistry, a list of major physical chemist at all German universities located here.
Subregions
Physical chemistry is divided into various sub- regions in which different phenomena to be investigated. The most important are theoretical chemistry, thermodynamics, kinetics, spectroscopy and electrochemistry.
Theoretical Chemistry
In theoretical chemistry, one tries to predict the properties of individual molecules or macroscopic quantities using mathematics or computer simulations and calculations. Quantum mechanics provides the basis for understanding the structure of matter and the chemical bond, while the Statistical thermodynamics provides the interconnection with the macroscopic thermodynamics.
Chemical Thermodynamics
The chemical thermodynamics unified energy terms of the electrochemical work (electromotive force ), thermal energy by increasing the temperature of a substance which work in gas expansion ( steam engine, internal combustion engine) and the thermal energy in conversion processes ( enthalpy, such as burning coal or gasoline).
The chemical thermodynamics allows statements, whether material reactions are possible which energies evolve at a reaction or need to be fed, which concentrations are to be expected with respect to products to reactants ( starting materials ) in accordance with the law of mass action if a temperature or pressure increase promotes the metabolism or damps, which redox potential or ion concentrations of individual substances can be expected.
Behavior of gases with temperature, volume, pressure changes
If the temperature change and constant external pressure, the volume of a gas varies in proportion to the temperature change. When the temperature rises, the gas expands at a cooling it contracts. The expansion factor is 1/273 per Kelvin. When a gas is compressed under high pressure, temperature, and internal energy of the gas increases. This internal energy of a gas can also submit work by the gas expands. This process has been used, for example, to drive steam engines. We extend a gas very quickly in a cylinder with a piston to a larger volume, so the gas cools. This process takes place for example in refrigerators or air liquefaction plants use. A steam engine, only a certain part of the heat energy into mechanical energy is converted. The heat energy is to work, however, the total energy of an isolated system does not change. The ratio of the heat energy component which is emitted to the environment unused in this process, the temperature is called entropy. Also, the outflow of gas into a vacuum is connected to an increase in entropy, the process is not running from voluntarily in the reverse direction.
Chemical transformations
Chemical transformations, the changes in the physical states or for dissolving salts or concentrated acids or bases in water are often connected to a heat or heat absorption. Previously, chemists believed that the heat development is based on that chemical reactions between substances occur. There were, however, later found also reactions in which occurred a cool down. Scientists realized that in transformations with heat loss had to play an important role in the entropy for chemical processes.
The amount of energy each of the transformation can be based on one mole of compound so that the results can be compared. 12 g during the combustion of carbon to carbon dioxide, 48 g of a different amount of heat ( enthalpy) is released as in the combustion of carbon 12 g to 28 g of carbon monoxide. Any material connection can - each based on one mole - a certain amount of energy ( standard enthalpy ) are assigned based on the measured heat energy. Unknown amounts of energy, such as the formation of carbon dioxide from carbon monoxide and oxygen can be determined by a summation. From the knowledge of the standard enthalpies of the chemist can determine how much heat energy is required at a stock at a conversion or reaction is free. The combustion of hydrogen gas and oxygen gas water and heat energy is produced. At the same time, the gas volume decreased. The gas abatement in this reaction is an energy quantity ( entropy) whose energy content is derived from the change of the gas volume as set out above. For the majority of substances the Standardbildungsentropie can been determined. Energetically the Standardbildungsentropie shall be determined by multiplying by the absolute temperature (in K). Standard enthalpy and Standardbildungsentropie are linked by the free enthalpy. By forming the differences of the Gibbs free energies of the final products to the starting materials, one obtains the free reaction enthalpy. The free enthalpy of reaction must always be negative, so that a reaction is possible, it is positive, is the chemical reaction impossible.
Law of mass action
The law of mass action - or, more precisely, the chemical equilibrium with the equilibrium constant K - describes the multiplicative combination of the concentrations of the products to the starting materials. A free enthalpy is linked by a single formula with the equilibrium constant of the mass action law. If the free reaction enthalpy is negative, formed primarily in the balance from the starting materials, the products; is the enthalpy of reaction is positive, almost no reaction takes place. By temperature or pressure changes in the balance of a chemical reaction can be frequently changed. Sometimes, however, catalysts are required, so that the equilibrium is as desired. Before the development of the Haber - Bosch process for the production of ammonia has been known from the thermodynamics, such that the formation of ammonia from hydrogen and nitrogen, should be possible. For a long time denied education, only by catalysts with higher temperatures and pressure, the reaction proceeded as desired from. The pressure was needed in order to compensate for the decrease in entropy, although a high temperature had a negative impact on the entropy, however, advantageous in the catalytic activation.
A particularly important law, the van't Hoff equation describes the equilibrium change as a function of the temperature change. Also, solubility of inorganic and organic salts in water and other liquids can be derived from the free reaction and the law of mass action to calculate. In redox reactions, the Nernst equation provides a means to calculate the concentration of ions or the electromotive potentials ( for example, of potassium permanganate in acidic, neutral and basic solution).
Kinetics
The kinetics is concerned with the temporal sequence of chemical reactions ( kinetics ) or by transport processes (eg, diffusion, material deposition on surfaces, catalysis ). In the kinetics of both the macroscopic course of a reaction ( macrokinetics ) and the exact course be a reaction in the individual elementary reactions studied ( microkinetics ).
Spectroscopy
Spectroscopy is a collective term for a class of experimental procedures that examine how a sample can absorb or emit energy in the form of electromagnetic radiation (radio waves, microwaves, infrared, visible light, ultraviolet, x-ray ). Goal of spectroscopy is to draw from the spectrum obtained conclusions to the test, for example, on their internal structure ( intermolecular force), material composition or dynamics.
Electrochemistry
Electrochemistry deals with the properties of charged particles, especially ions, and the effects of electric current on substances. The main research areas of electrochemistry are aqueous solutions of ions, called electrolyte, and the operations at the interface between the electrolyte and electrodes. Technically important applications of electrochemistry are the fuel cell and the deposition of metals on surfaces in electroplating.
Relevance in the art and in everyday life
Physical chemistry deals with many objects that hold great potential for application or of decisive importance for the quality of life of humanity.
- In the field of reaction kinetics Paul J. Crutzen, Mario J. Molina and Frank Sherwood Rowland were awarded the Nobel Prize for their research on the reaction mechanism of the formation and decomposition of ozone.
- In virtually every car a lambda probe operating in the catalyst which continuously carries out a flue gas analyzer and adjusts the fuel injection so as to eject a minimum of unburned fuel and thus increase the efficiency.
- For the development of new batteries for laptops and mobile phones electrochemical knowledge is essential.
- In the area of drug development for the pharmaceutical industry, more and more methods of theoretical chemistry are used.
- Physical chemistry is one of the key disciplines of nanotechnology.
- The methods of surface chemistry provide insights into the process of ammonia synthesis, without artificial fertilizer production is not possible and the global food production would be far more difficult.