principles of chemical kinetics

[...]... studying the rate of the reaction If a reaction takes place in a series of steps, a study of the rate of the reaction gives information about the slowest step of the reaction We can 4 Principles of Chemical Kinetics see an analogy to this in the following illustration that involves the flow of water, H2O in 3'' 1'' 5'' H2O out If we study the rate of flow of water through this system of short pipes,... of this book is to provide the background in the principles of kinetics that will enable him or her to interpret the results The capability of the available software to perform numerical analysis is a separate issue that is not addressed in this book 1.1 RATES OF REACTIONS The rate of a chemical reaction is expressed as a change in concentration of some species with time Therefore, the dimensions of. .. concentration of A, has some fixed value so it is a constant Therefore, Eq (1.14) can be put in the 6 Principles of Chemical Kinetics form of a linear equation where y ¼ ln[A], m ¼ Àk, and b ¼ ln [A]o A graph of ln[A] versus t will be linear with a slope of Àk In order to test this rate law, it is necessary to have data for the reaction which consists of the concentration of A determined as a function of time... usually be determined experimentally Chemical kinetics is largely an experimental science Chemical kinetics is intimately connected with the analysis of data The personal computers of today bear little resemblance to those of a couple of decades ago When one purchases a computer, it almost always comes with software that allows the user to do much more than word processing Software packages such as Excel,... rates, at least not directly The preceding example shows that the thermodynamics of the reaction favors the production of water; however, kinetically the process is unfavorable We see here the first of several important principles of chemical kinetics There is no necessary correlation between thermodynamics and kinetics of a chemical reaction Some reactions that are energetically favorable take place very... surface of the Fundamental Concepts of Kinetics 11 catalyst What does matter in this case is the surface area of the catalyst As a result, the decomposition of OClÀ on a specific, fixed amount of catalyst occurs at a constant rate over a wide range of OClÀ concentrations This is not true as the reaction approaches completion, and under such conditions the concentration of OClÀ does affect the rate of the... half-life is independent of the initial concentration of the reactant, but in the case of a second-order reaction, the half-life is inversely proportional to the initial concentration of the reactant 1.2.3 Zero-Order For certain reactions that involve one reactant, the rate is independent of the concentration of the reactant over a wide range of concentrations For example, the decomposition of hypochlorite... of the observations regarding the study of reaction rates is that a rate cannot be calculated from first principles Theory is not developed to the point where it is possible to calculate how fast most reactions will take place For some very simple gas phase reactions, it is possible to calculate approximately how fast the reaction should take place, but details 1 2 Principles of Chemical Kinetics of. .. sufficient amount to replace quickly that which reacts on the surface of the catalyst Therefore, the concentration of OClÀ does limit the rate of reaction in that situation, and the reaction is no longer independent of [OClÀ ] The rate of reaction is independent of [OClÀ ] over a wide range of concentrations, but it is not totally independent of [OClÀ ] Therefore, the reaction is not strictly zero-order,... using linear regression (the method of least squares) In this method, a calculator or computer is used to calculate the sums of the squares of the deviations and then the ‘‘line’’ (actually a numerical relationship) is 14 Principles of Chemical Kinetics 0 −0.2 −0.4 ln [A] −0.6 −0.8 −1.0 −1.2 −1.4 −1.6 −1.8 FIGURE 1.6 0 10 20 30 40 50 Time, min 60 70 80 90 A plot of ln[A] versus time for data that has . unfavorable. We see here the first of several important principles of chemical kinetics. There is no necessary correlation between thermodynamics and kinetics of a chemical reaction. Some reactions. as aA þbB ! cC þdD(1:3) 2 Principles of Chemical Kinetics the rate law will usually be represented in terms of a constant times some function of the concentrations of A and B, and it can usually. book. 1.1 RATES OF REACTIONS The rate of a chemical reaction is expressed as a change in concentration of some species with time. Therefore, the dimensions of the rate must be those of concentration