Why Are We Proud to Be Kineticists?
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id2486640 pdfMachine by Broadgun Software - a great PDF writer! - a great PDF creator! - http://www.pdfmachine.com http://www.broadgun.com gl bal S c ie n t ific In c . ChemXpress gl bal S c ie n t ific In c . From Editorial Desk Why are we proud to be Kineticists? R.Sanjeev1, V.Jagannadham*2 1Department of Chemistry, Mizan-Tepi University, Tepi Campus, (ETHIOPIA) 2Department of Chemistry, Osmania University, Hyderabad-500 007, (INDIA) E-mail: [email protected] In the recent past for the last four to five years, of chemical kinetics. They look down the subject of when we used to attend some departmental confer- chemical kinetics. But as we understood, like math- ences, some scientific meetings and PhD viva-voce ex- ematics which is the mother of science, we can proudly aminations, in the lunch break or in the tea break tim- say that chemical kinetics is the mother of chemical sci- ings some teachers so called modern day chemists whom ence. This is well understood by the following diagram we knew very well and who do the research in solid by any average chemist or chemistry teacher or by a state chemistry and drug discovery used to talk to us ill freshmen college student. 6E0 ditorial Desk ChemXpress 2(2), 2013 From the diagram it is very clear that the subject The reaction in question was the inversion of cane of chemical kinetics can not simply keep quite with- sugar. The name originates from a prior study by Biot out peeping and interacting through almost all branches and Persoz who used the polarimeter to study the re- of chemistry including pharmacology. Some of the action. lightning facts give the support to this contention by The solution of cane sugar which rotates the plane “Nobel Prizes” to several virtue of being awarded polarized light to the right but which rotates it to the left Scientists working in Reaction Dynamics or Chemical on the addition of a dilute acid. It was found chemically Kinetics. The events of Nobel Laureates who were that cane sugar absorbs the elements of water and “Reaction awarded Nobel Prizes for their work in changes into a mixture of two different sugars, one be- ” with their names, pho- Dynamics/Chemical Kinetics ing weakly dextrorotatory and the other strongly tographs and their discoveries are being summarized laevorotatory, hence the resultant is a rotation to the chronologically in the following, at first starting with a left. At the same time these workers observed that the small introduction. process is not completed instantaneously but requires a The processes grouped together by Berzelius were: period of time varying with the nature and concentra- The transformation of starch into dextrin and sugar tion of the added acid. Biot who, as a physicist, was by acids (Kirchhoff, 1811). more readily inclined than all the chemists of his day The same transformation by malt extract (Kirchhoff, (Wilhelmy too was a physicist) to regard the observed 1814). phenomenon as a systematic transient process, also The decomposition of hydrogen peroxide into wa- pointed out the importance of a more thorough investi- ter and gaseous oxygen in the presence of platinum, gation of these phenomena. However, only Wilhelmy énard, 1818). manganese dioxide, etc. (Th was sufficiently interested to undertake not only the The action of finely divided platinum on inflammable necessary experiments, but in particular also the funda- öbereiner, 1823). gas mixtures (Davy, 1817; and D mental task of formulating the concepts. ’s work (1850) in chemical kinetics con- The formation of ether by the action of sulphuric Wilhelmy acid (Mitscherlich, 1834). cerned the acid-catalyzed conversion of a sucrose so- The factor which Berzelius regarded as being com- lution into a 1:1 mixture of fructose and glucose, a re- mon to all these processes was that the substances which action that he followed with a polarimeter. He wrote a interact to form the product do not do so on their own differential equation to describe the reaction, integrated or spontaneously but only after the addition of a certain it, and used it to interpret his experimental results. ’s rate was propor- substance which is not itself consumed. Wilhelmy found that the reaction Mitscherlich had termed the process which he stud- tional to the concentrations of sucrose and of acid ied is a chemical action by contact; Berzelius intro- present. The ratio of the amount of substance (cane duced the name catalysis instead, with the active but sugar in this case) converted in a given time to the time unconsumed substance being termed the catalytic sub- required for the process he conceived and defined as a stance or catalyst, and the cause underlying the phe- new concept, the rate of chemical reaction, recog- nomena catalytic force. nizing its appropriate mathematical definition at once to The development of a rational view of the nature of be the differential quotient of the amount of substance catalysis was thus absolutely dependent on the creation with respect to time. of the concept of the rate of a chemical reaction. The Wilhelmy then demonstrated that on the simplest concept was formulated (after an inadequate attempt assumption that the amount of sugar converted under by Berthollet) by the German amateur scientist Wilhelmy the given conditions in each element of time is propor- and by a remarkable chance (or is it the intrinsic logic tional to the amount remaining unchanged, there is a of historical evolution?) the first paper to submit a proper large measure of agreement between the observed concept of the rate of a chemical reaction also consti- changes in rotation and those calculated on the basis of tutes the first quantitative study of a process proceed- this assumption, and thus he discovered the general law ing under catalytic action. for the time dependence of the chemical processes. It ChemXpress 2(2), 2013 Editorial Desk61 has subsequently proved to be the fundamental law of gree hitherto undreamed-of. chemical kinetics. Svante Arrhenius 1902 Ostwald found that methyl acetate proved even more suitable owing to its greater solubility and faster This, the second of Nobel Laure- reaction rate, and so one of his first studies in chemical ates in chemical dynamics, features the dynamics, in 1883, dealt right away with a catalytic pro- work of Svante Arrhenius, who won cess, i.e. the catalytic saponification of this particular the Nobel Prize in 1902 for his elec- ester under the action of various acids. trolytic theory of dissociation. Although it was not mentioned specifically in his The Nobel Prize was awarded 15 times, to a total Arrhenius of 24 recipients, for work involving various aspects of Nobel presentation, the well-known ’t Hoff chemical dynamics beginning with Jacobus van Arrhenius equation relating reaction rate constants to in 1901, out of a total of 161 recipients in Chemistry activation energies and temperature is fundamental to which is 18% of the total Nobel Prizes went to the people all subsequent studies of reaction energetics and ca- working on Chemical Dynamics or Chemical Kinetics. talysis, and no modern discussion of chemical dynam- Had the award of Nobel Prizes started a century ics could begin without it. Arrhenius is best remembered before, about a dozen scientists like Berzelius, today by teachers and students of chemistry because énard, Davy, Döbereiner, Mitscherlich, Kirchhoff, Th the definition of acids and bases and also the equation Berthollet, Biot, Persoz and Wilhelmy more would have k = A e-Ea/RT relating reaction rate constants to tempera- been awarded Nobel Prizes in Chemical Kinetics. ture through the activation energy that are both named ’ for him. J.H.van t Hoff 1901 Wilhelm Ostwald 1909 The first Nobel Prize went to a Physical Chemist in1901, who is none The third Nobel Laureates in ’T HOFF for his work other than VAN chemical dynamics, features the work on Chemical Dynamics in recognition of Wilhelm Ostwald, who won the of the extraordinary services he has Nobel Prize in 1909 for his work on catalysis, equilibriums, and reaction ’ rendered by the discovery of the laws ’s name remains asso- van t Hoff rates. Ostwald of chemical dynamics and osmotic Ostwald pressure in solutions. He discovered how to express ciated with the catalytic process used the state of chemical equilibrium in reactions and the to manufacture nitric acid from ammonia. electromotive force which a reaction can produce; he George de Hevesy 1943 explained how the transition occurs between the vari- ’t Hoff’s investi- The fourth Nobel Prize for re- ous modifications of the elements. van search related directly to chemical dy- gations showed that the law, which has been named namics was awarded to George de after the Italian Avogadro, according to which the num- “for his work on the Hevesy in 1943 ber of gas molecules in a given volume is the same for use of isotopes as tracers in the study all gases at the same pressure and temperature, em- ”. of chemical processes braces not only substances in the gaseous phase but Hevesy also those in solution, provided that their pressure, Hinshelwood and known as osmotic pressure, is taken into account in the Semenov 1956 same way as the gas pressure in the case of gases. He proved that gas pressure and osmotic pressure are iden- This is the fifth tical, and thereby that the molecules themselves in the Nobel Prize in che- gaseous phase and in solutions are also identical. As a mical dynamics dur- result of this the concept of the molecule in chemistry ing the 20th century. was found to be definite and universally valid to a de- Hinshelwood Semenov Cyril Hinshelwood .