Chemical action, rate

Complex chemical mechanisms are written as sequences of elementary steps satisfying detailed balance where tire forward and reverse reaction rates are equal at equilibrium. The laws of mass action kinetics are applied to each reaction step to write tire overall rate law for tire reaction. The fonn of chemical kinetic rate laws constmcted in tliis manner ensures tliat tire system will relax to a unique equilibrium state which can be characterized using tire laws of tliennodynamics. 

For a closed chemical system witli a mass action rate law satisfying detailed balance tliese kinetic equations have a unique stable (tliennodynamic) equilibrium, In general, however, we shall be concerned witli... 

Electrochemical corrosion is understood to include all corrosion processes that can be influenced electrically. This is the case for all the types of corrosion described in this handbook and means that data on corrosion velocities (e.g., removal rate, penetration rate in pitting corrosion, or rate of pit formation, time to failure of stressed specimens in stress corrosion) are dependent on the potential U [5]. Potential can be altered by chemical action (influence of a redox system) or by electrical factors (electric currents), thereby reducing or enhancing the corrosion. Thus exact knowledge of the dependence of corrosion on potential is the basic hypothesis for the concept of electrochemical corrosion protection processes. 

Corrective Action Check pump and meter settings. Conflrm thast setting correspond with anticipated chemical feed rates. 

In these equations the independent variable x is the distance normal to the disk surface. The dependent variables are the velocities, the temperature T, and the species mass fractions Tit. The axial velocity is u, and the radial and circumferential velocities are scaled by the radius as F = vjr and W = wjr. The viscosity and thermal conductivity are given by /x and A. The chemical production rate cOjt is presumed to result from a system of elementary chemical reactions that proceed according to the law of mass action, and Kg is the number of gas-phase species. Equation (10) is not solved for the carrier gas mass fraction, which is determined by ensuring that the mass fractions sum to one. An Arrhenius rate expression is presumed for each of the elementary reaction steps. 

In some cases, e.g. the oxidation of hydrocarbons by potassium permanganate (Meyer and Saam, Ber. xxx. 1935, 1897), the hydrolysis of emulsions of esters in water CGoldschmidt, Zeit. Phys. Ghem. xxxi. 235, 1899), and the dissmution of arsenious oxide (Drucker, Zeit. Phys. Ghem. xxxvi. 693, 1901), the actual chemical reaction between solvent and solute appears to be slower than the process of diffusion, and thus the rate of chemical action is independent of the diffusion coefficient. 

This chapter sets out the basic formulation and governing equations of mass-action kinetics. These equations describe the time evolution of chemical species due to chemical reactions in the gas phase. Chapter 11 is an analogous treatment of heterogeneous chemical reactions at a gas-solid interface. A discussion of the underlying theories of gas-phase chemical reaction rates is given in Chapter 10. 

Chemical kinetics govern the rate at which chemical species are created or destroyed via reactions. Chapter 9 discussed chemical kinetics of reactions in the gas phase. Reactions were assumed to follow the law of mass action. Rates are determined by the concentrations of the chemical species involved in the reaction and an experimentally determined rate coefficient (or rate constant) k. 

Although slowly progressing chemical changes attracted the attention of the earliest and most superficial observers, no definite ideas about the intimate nature of chemical action could be formed until quantitative investigations on the rate of progress of reactions were made. Such investigations were first made by Harcourt and Esson and by Wilhelmy. Their work, and that of van t Hoff on chemical dynamics, laid the foundations of the whole subject. 

At high pressure methane becomes thermodynamically stable and does not enter into endothermic reactions which are accompanied by an increase in the number of molecules. Under these conditions the flegmatizing action of excess methane proves weak. Evidently, the higher heat capacity of methane is compensated for by the increase in the chemical reaction rate for increased methane concentration. 

Calculations show that addition of CC14 has practically no influence on the combustion temperature and that its flegmatizing action depends on its influence on the chemical reaction rate. 

In addition, at the point where Jouguet s condition (29) or (6) is satisfied, the chemical reaction has not yet completed = 1 corresponds to a particular chemical reaction rate which balances the action of heat transfer... 

In slow flame propagation its velocity is determined by the maximum chemical reaction rate at a temperature close to the maximum temperature of combustion the zone of low temperature and small reaction rate is overcome by the action of heat conduction. 

In photocatalytic reactions the variations in the bond strength of the surface bonds due to photoexcitation are traced by the chemical action of the bonds, i.e. by changes of rate and by changes of reaction pathway of the reactions involving the bonds at the surface. 

Because of their variable thermodynamic state and concentration each reactant or product is characterized at any instant by an intrinsic activity, a, and the interplay between these activities defines the chemical action A, at that instant. The action changes at a rate proportional to A and to the change in affinity, as summarized by the linear homogeneous equation ... 

Other experiments were carried out also on the decomposition of carbon dioxide, the decomposition of hydrochloric acid gas and the oxidation of alcohol vapor. In no case was chemical action brought about by the absorption of an intense beam of infrared radiation. Furthermore, no case of chemical reactivity produced by longer infrared radiation has been established in the literature. Increases in reaction rates in early experiments can be traced to an increase in the temperature of the solution produced by the absorption of the heat rays. A few cases of activity of short infrared rays of 1 jx and less are on record in special reactions. 

Oxidation processes arc, as a general rule, greatly accelerated by a rise in temperature the first effect of the application of heat may be merely to initiate a slow oxidation which soon ceases on the removal of the source of heat but a higher temperature may cause so marked an increase m the rate of the chemical action that the heat produced suffices to maintain the temperature, and the oxidation or combustion will proceed unaided. This temperature at which the process of rapid combustion becomes independent of external supplies of heat is termed the ignition temperature of the substance (see p. 106). Phosphorus does not commence rapid combustion until a temperature of 60° C. is attained hydrogen will combine, albeit excessively slowly, with oxygen already at 180° C., but the reaction is not very appreciable below 400° C., and continuous inflammation does not occur until near... 

Rise in temperature is, in practice, the simplest process for inducing chemical action between hydrogen and oxygen. It is supposed by some chemists that the absence of chemical action in detonating gas at the ordinary temperature in the absence of light or of radioactive substances is only apparent, the actual rate of combination merely being too small for detection by the usual methods with increase in temperature the combination is accelerated so that it becomes perceptible or even explosive. The necessary heat can be applied in... 

Inhibitor (of an electrode reaction) — is a substance that added to the electrolyte solution causes a decrease in the rate of an electrochemical process by a physical, physicochemical, or chemical action and, generally, by modifying an electrode surface. This modification is due to adsorption of the inhibitor. The inhibitor may play no direct role in the electrochemical reaction or it can be a reaction intermediate. 

Chemical reaction rate depends on the collisions of molecules, per second per unit volume. Since the number of collisions of a species is proportional to its concentration, the chemical reaction rate is proportional to the product of concentrations (mass action law). Thus, for a single homogeneous elementary chemical reaction... 

Experimental evidence strongly suggests that material removal in chemical-mechanical polishing (CMP) processes is a result of one or more chemical steps that alter the wafer surface combined with a mechanical step that removes the altered material. Chemical action by itself also removes material by static etching, but generally at a much lower rate than is observed when mechanical action is also present. Similarly, polishing rates observed when a minimally reactive fluid such as water is used instead of slurry are also low. Both chemical and mechanical processes are therefore involved in material removal at commercially practical rates, and the model we describe reflects this dual nature of the process. 

There have been some efforts in slurry recycling to reduce CoO of CMP consumables. In a recent study [37], the effluent samples were characterized for pH, trace-metal levels, viscosity, specific gravity, mean aggregate particle size, and LPC (>1.0 rm) before and after depth (melt-blown polymeric media) filtration. The study showed that the use of a recycled fumed silica slurry (recycled five times) decreased the CMP removal rate and the coefficient of friction (COF) by 40%. A perfect relationship was observed between the removal rate and COF. It was concluded that the increase in mean aggregate particle size, which lowers the contact area between the abrasive particles and the wafer, had some impact on the removal rate data. In general, there is a stronger emphasis on slurry additives and chemical action in current CMP processing with much lower maximum defectivity performance specifications [2]. 

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