Thermodynamics versus kinetics

How can we understand the difference between thermodynamics and kinetics Here is a simple way to think about the two subjects Thermodynamics predicts what should happen, kinetics predicts how fast it will happen. 

The relative thermodynamic stability of graphite versus diamond provides a classic illustration of the interplay between thermodynamics and kinetics. Graphite and diamond are both polymorphs (same composition but different phases) of carbon. At room temperature and pressure, thermodynamics tells us that diamond is less stable than graphite—in other words, there is an energetic driving force favoring the transformation of diamond into graphite. So, are diamonds forever Thermodynamics 

FIGURE 1.2 Schematic illusiTation of the interplay between thermodynamics and kinetics. Thermodynamics can be used to quantify departures from equiUbrium and hence the driving forces acting on a system to return it to equilibrium. Kinetics can be used to determine the pathway and the speed at whieh a system returns to equilibrium. Many different seenarios are possible, from extremely fast equilibration to rates so slow that they are essentially zero. 

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Of all the functions of proteins, catalysis is probably the most important. In the absence of catalysis, most reactions in biological systems would take place far too slowly to provide products at an adequate pace for a metabolizing organism. The catalysts that serve this function in organisms are called enzymes. With the exception of some RNAs (ribozymes) that have catalytic activity (described in Sections 11.7 and 12.4), aU other enzymes are globular proteins (section 4.3). Enzymes are the most efficient catalysts known they can increase the rate of a reaction by a factor of up to 10 ° over uncatalyzed reactions. Non-enzymatic catalysts, in contrast, typically enhance the rate of reaction by factors of 102 to 104 

Traveling over a mountain pass is an analogy frequently used to describe the progress of a chemical reaction. Catalysts speed up the process. 

The reaction of glucose and oxygen gas to produce carbon dioxide and water is an example of a reaction that requires a number of enzymatic catalysts  

This reaction is thermodynamically favorable (spontaneous in the thermodynamic sense) because its free energy change is negative AC = -2880 kj moH = -689 kcal mol ). 

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Basic Mechanistic Concepts Kinetic versus Thermodynamic Control, Hammond s Postulate, the Curtin-Hammett Principle... 

SECTION 4.4. BASIC MECHANISTIC CONCEPTS KINETIC VERSUS THERMODYNAMIC CONTROL, HAMMOND S POSTULATE. THE CURTIN-HAMMETT PRINCIPLE... 

The idea of kinetic versus thermodynamic control can be illustrated by discussing briefly the case of formation of enolate anions from unsymmetrical ketones. This is a very important matter for synthesis and will be discussed more fully in Chapter 1 of Part B. Most ketones, highly symmetric ones being the exception, can give rise to more than one enolate. Many studies have shown tiiat the ratio among the possible enolates that are formed depends on the reaction conditions. This can be illustrated for the case of 3-methyl-2-butanone. If the base chosen is a strong, sterically hindered one and the solvent is aptotic, the major enolate formed is 3. If a protic solvent is used or if a weaker base (one comparable in basicity to the ketone enolate) is used, the dominant enolate is 2. Enolate 3 is the kinetic enolate whereas 2 is the thermodynamically favored enolate. 

FIGURE 6.3 Free energy profile illustrating kinetic versus thermodynamic control of product. The starting compound (A) can react to give either B or C. 

Directions for Future Work. The measurement of rates of proton transfer from a single acid to more bases differing only in thermodynamic base strength should allow the construction of BrjSnsted plots of kinetic versus thermodynamic acidity. The bases we have used at this early stage of development of the subject have involved different proton acceptor atoms and cannot be so used (although comparison of the Et N transfer rates of... 

Schicks, J.M. Ripmeester, J.A. (2002). The Coexistence of Two Different Methane Hydrate Phases under Moderate Pressure and Temperature Conditions Kinetic versus Thermodynamic Products. Angew. Chem. Int. Ed., 43,3310-3313. 

This chapter provides a general discussion of kinetics versus thermodynamics, chemical kinetics versus geochemical kinetics, and an overview of the basics of various kinetic processes and applications. Subsequent chapters will provide in-depth development of theories and applications of specific subjects. The purpose of the overview in this chapter is to provide the big picture of the whole field before in-depth exploration of the topics. Furthermore, this chapter is a standalone chapter that may be used in a general geochemistry course to introduce kinetics to students. 

In a picosecond spectroscopic study of kinetic versus thermodynamic hydrogen atom transfer from N-methylacridan 14,... 

Another example in which the regioselectivity of addition is different under kinetic versus thermodynamic control is the naphthalene series. In the addition of LiCMe2CN to [(naphthalene)Cr(CO)3] (41), a mixture of products is observed from addition at C-a and C-(3 in the ratio 42 58 under conditions where equilibration is minimized (0.3 h, -65 C, THF-HMPA). With the same reactants, but in THF and at 0 °C, the product is almost exclusively the a-substituted naphthalene (equation Sti).84-83 92... 

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