Chemical changes conditions affecting rate

CHEMICAL REACTION RATE. The chemical composition of a substance is subject to various changes under various conditions, depending upon (l)thc nature of the specific substance. (2) the nature of other substances present, and (3) the environment in which it exists (the physical and chemical ambient conditions). Similarly, chemical reaction rales are affected. 

To predict how changes in the conditions affect the rate of a chemical reaction... 

Concentration of Chemical Species Units of (moles/Iiter). Reaction rates are determined by both the concentrations of the reactants and the products of a reaction. Slurry chemicals either supply reactants or remove products, and hence as the concentration of the slurry chemicals increases, the reaction rates increase. Note, however, that the overall CMP process is composed of several steps and several different reactions. For any given set of process conditions, one of these steps will be limiting the total CMP removal rate. If an individual reaction is not part of this rate limiting step, the polish rate will be unaffected by changing the reaction rate. Only the reactions that are part of the rate limiting step will affect the polish rate. 

The goal of the analyses discussed in this section is to identify and determine the mechanism and kinetics of transient chemical processes that can affect the dynamic performance of an automotive catalyst. By "transient" we mean that the conversion due to the process changes at a rate that is somewhat slower than the rate of change in conditions during driving. That is, the... 

The frequency scan is used for several purposes that will be discussed in this section. One very important use, that is very straightforward, is to survey the material s response over various shear rates. This is important because many materials are used under different conditions. For example adhesives, whether tape, Band-Aids, or hot melts, are normally applied under conditions of low frequency and this property is referred to as tack. When they are removed, the removal often occurs imder conditions of high frequency called peel. Different properties are required at these regimes and to optimize one property may require chemical changes that harm the other. Similarly, changes in polymer structure can show these kinds of differences in the frequency scan. For example, branching affects different frequencies (9). 

Another reason for studying reaction rates is to understand how chemical reactions occur. By noting how the rate of a reaction is affected by changing conditions, you can sometimes learn the details of what is happening at the molecular level. 

A summary of the chemical and abrasion resistances, and approximate operational temperature ranges of elastomers is given in Table 18.16. Further details of specific chemical resistances are given in Table 18.17. The maximum temperature of use will always be dependent on the chemical conditions prevailing. Abrasion resistance can be affected by the chemical environment if the exposed surface properties are changed by adsorption or chemical attack. The rate of material loss by abrasion will also vary according to temperature as the resilience etc. is dependent on prevailing temperature conditions. 

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