Reactant chemical reactions dependence

From the coverage made thus far, it may be of interest to record in one place the different factors which influence the rate of chemical reactions. The rate of chemical reaction depends essentially on four factors. The nature of reactants and products is one. For example, certain physical properties of the reactants and products govern the rate. As a specific example in this context mention may be of oxidation of metals. The volume ratio of metallic oxide to metal may indicate that a given oxidation reaction will be fast when the oxide is porous, or slow when the oxide is nonporous, thus presenting a diffusion barrier to the metal or to oxygen. The other two factors are concentration and temperature effects, which are detailed in Sections. The fourth factor is the presence of catalysts. 

The rate of a chemical reaction depends on what the reactants are. 

The rate of a chemical reaction depends on several factors, as you learned in section 6.1. One of the factors that affect reaction rate is the concentrations of the reactants. You know that the rates of most chemical reactions increase when the concentrations of the reactants increase. Is there a more specific relationship In this section, you will explore the quantitative relationships between the rate of a reaction and the concentrations of the reactants. 

The overall effect of the preceding chemical reaction on the voltammetric response of a reversible electrode reaction is determined by the thermodynamic parameter K and the dimensionless kinetic parameter . The equilibrium constant K controls mainly the amonnt of the electroactive reactant R produced prior to the voltammetric experiment. K also controls the prodnction of R during the experiment when the preceding chemical reaction is sufficiently fast to permit the chemical equilibrium to be achieved on a time scale of the potential pulses. The dimensionless kinetic parameter is a measure for the production of R in the course of the voltammetric experiment. The dimensionless chemical kinetic parameter can be also understood as a quantitative measure for the rate of reestablishing the chemical equilibrium (2.29) that is misbalanced by proceeding of the electrode reaction. From the definition of follows that the kinetic affect of the preceding chemical reaction depends on the rate of the chemical reaction and duration of the potential pulses. 

We noted in Section 12.1 that the rate of decomposition of N205 depends on its concentration, slowing down as the N205 concentration decreases. Ordinarily, the rate of a chemical reaction depends on the concentrations of at least some of the reactants. 

As pointed out earlier, the AG of a chemical reaction depends not only on the AGq but also on the initial concentrations of reactants and products. Thus, in rat muscle, whereas [ATP] = [ADP] = 8 x 10 3M, [P(] = 0.9 x 10 3M. At37°C, AG of this system is potentially -13,310 cal/mol, and it is evident that under the in vivo conditions of the rat muscle, ATP can deliver quite a bit more energy than would be predicted from its AGq. 

The amount of heat required for a specific chemical reaction depends on the temperatures of both the reactants and products. A consistent basis for treatment of reaction heat effects results when the heat of reaction is defined as the heat effect that results when all products and reactants are at the same temperature. 

Both the rate and tire equilibrium conversion of a chemical reaction depend on the tem-peraUire, pressure, and compositionof reactants. Consider,for example, the oxidation of sulfur dioxide to sulfur trioxide. A catalyst is required if a reasonable reaction rate is to be attained. Witli a vanadium pentoxide catalyst the rate becomes appreciable at about 573.15 K (300°C) and continues to mcrease at higher temperatures. On the basis of rate alone, one would operate tire reactorat the highest practical temperature. However, the equilibrium conversion to sulfur trioxide falls as temperature rises, decreasing from about 90% at 793.15 K (520°C) to 50% at about 953.15 K (680°C). These values represent maximum possible conversions regardless of catalyst or reaction rate. The evident conclusion is that both equilibrium and rate must be considered in the exploitation of chemical reactions for commercial purposes. Although reaction rates are not susceptible to thermodynamic treatment, equilibrium conversions are. Therefore, the purpose of this chapter is to detennine the effect of temperature, pressure, and initial composition on the equilibrium conversions of chemical reactions. 

What conclusion can you draw about how the rate of a chemical reaction depends on the concentration of the reactants ... 

The specific rate of a chemical reaction depends on the standard free energy difference between reactants and the transition state the problem of the influence of the solvent on reaction rates therefore reduces to the determination of the free energies, entropies and enthalpies of solvation of the reactants and of the transition state (Benson, 1960 Reichardt, 1965 Leffler and Grunwald, 1963 Wiberg, 1984 Laidler, 1950 Arnett et al., 1965). 

The forward rate of a chemical reaction depends on the concentrations of the reactants. As an example, consider the decomposition of gaseous dinitrogen pen-taoxide (N2O5). This compound is a white solid that is stable below 0°C but decomposes when vaporized ... 

The rates of all chemical reactions depend on the concentrations of reactants. This concentration dependence is expressed in the empirical rate law in which the rate is proportional to the concentration of reactants raised to some power. The power is not necessarily related to the stoichiometric coefficient in the balanced reaction. 

The rate of a chemical reaction is, in a dilute solution, proportional to the concentrations of the various reactants each raised to the power of the number of moles of the reactant in the balanced chemical equation. This sounds too easy, and in fact it is. In practice, the rate of a chemical reaction depends only on a small number of concentration terms, and the sum of the powers to which these concentrations are raised is termed the order of the reaction. This is because chemical reactions occur in a number of steps, or stages (called a mechanism) and the rate of the overall reaction is often governed by the rate of the slowest step (called, not surprisingly, the ratedetermining step). Even if every other stage of a chemical reaction occurs essentially instantaneously, the rate of the reaction as a whole cannot exceed that of the slowest stage. 

Chemical reaction depends on the presence of reactive substrates and on the probability of their encounters. Thus, the possibilities of reactions can be numerous. The literature describes reactions of OH groups on the surface of kaolin with isocyanates, vulcanization of nitrile rubber by ZnO, reactions of carboxyl groups on the filler surface with amines and epoxy groups, reactions of carboxyl groups with diols," and many others.The presence of a reactant on the surface of a material particle increases the probability of chemical reaction. Other factors include statistical probabilities, surface barriers which affect contact, dilution factors, molecular mobility, and viscosity changes in the system. These are discussed in other sections of this book. 

The entropy change associated with a chemical reaction depends on the nature of the reactants and products. The reaction... 

After the introduction of rate of reaction we have seen how a chemical reaction depends of other things than stoichiometry. It is thereby reasonable to assume that the temperature also plays a significant role for the cause and velocity of reaction. This combination is described by the Arrhenius-equation named after the Swedish chemist Svante Arrhenius due to his work on reaction kinetics in the 1880 ies. The Arrhenius-equation gives the connection between temperature, reaction constant and the concentration of reactant in the following manner ... 

These data show that we cannot conclude that two-step cycles will always be faster just because they have smaller activation energies the rates of chemical reactions depend on concentrations of reactants as well as magnitudes of rate constants. For the same reason, all four catalytic cycles have reaction (6) as the rate limiting reaction, even though it has the smaller activation energy. 

The heat associated with a chemical reaction depends on the pressure and temperature at which the reaction is carried out. All thermochemical data presented here are for reactions carried out under standard conditions, which are a temperatnre of 298 K (24.85°C) and an applied pressure of one bar. The quantity of heat released in a reaction depends on the amount of material undergoing reaction. The chemical formulas that appear in a reaction each represent 1 mole (see article on Mole Concept ) of material for example, the symbol CH4 stands for 1 mole of methane having a mass of 16 grams (0.56 ounces), and the 2 02(g) tells us that 2 moles of oxygen are required. Thermochemistry also depends on the physical state of the reactants and products. For example, the heat liberated in equation (1) is 890... 

The rate of a chemical reaction depends on how quickly reactants are consumed or, alternatively, how quickly products are formed. By convention, rates of reaction, rates of consumption, and rates of production are always reported as positive numbers. 

We commence the chemical reaction once the liquid inside a batch or semi-batch reactor reaches reaction temperature. The time required to complete the chemical reaction depends upon the chemical kinetics of the reaction mechanism and the desired final product concentration or reactant concentration. For a first-order reaction, the time required to reach a given product concentration is... 

The kinetics of chemical reactions can provide many clues as to the nature of the bond-breaking and bond-making processes on the molecular level that lie at the core of any reaction mechanism. The reaction rate can be defined as the differential rate of loss of a reactant or the differential rate of formation of a product as a function of time. The rates of chemical reactions depend on a variety of factors, including the concentrations of the reactants, ionic strength, temperature, surface area, and... 

At the instant we initiate a chemical reaction between two reactants, there are no products present (Figure 12.5). We have already seen that the rate of a chemical reaction depends on the concentrations of reactants, so initially the rate of the reverse reaction must be zero, because the concentrations of its reactants—which are the products of the forward reaction—are zero. Thus when we first mix the reactants, the rate of the forward reaction is greater than that of the reverse reaction. Over time, the concentrations of the reactants decrease, and those of the products increase. These changes in concentration are accompanied by changes in rate the forward reaction slows down and the reverse reaction speeds up. Ultimately, chemical equilibrium is reached when the two rates become equal, and the observable concentrations of both reactants and products become constant. In any... 

The manner in which the rate of a chemical reaction depends on the concentration of the reactants must be determined experimentally. Many simple, one-step reactions result from a collision between two molecules or ions. The rate of such one-step reactions can be altered by changing the concentration of the reactants or products. An increase in concentration of the reactants provides more individual reacting species for collisions and results in an increase in the rate of reaction. 

The reaction rate is defined as the number of reactive events per second per unit volume. It is usually expressed as molL s . Chemical reactions depend on collisions. In most reactions, only a very small fraction of the collisions result in a chemical reaction. For each reacting species, since the number of collisions per unit volume is proportional to its concentration, the rates are proportional to the product of the concentrations. A reaction rate refers to conversion of the reactants to the products or vice versa. Thus, for the reaction... 

How increasing the polarity of the solvent (that is, increasing its dielectric constant) will affect the rate of most chemical reactions depends only on whether or not a reactant in the rate-limiting step is charged ... 

We have seen that the rate of a chemical reaction depends on the energy barrier of the rate-determining step that must be overcome in the process of converting reactants into products. The height of the energy hill is indicated by the free energy of activation (AG ). A catalyst increases the rate of a chemical reaction by providing a pathway with a lower AG (Section 5.11). A catalyst can decrease AG in one of three ways ... 

The method of discussing chemical reactivity represented by theories of the type discussed above cannot in general be justified. The rate of a chemical reaction depends on the difference in energy between the reactants and the transition state for the reaction s. In principle, then, it is essential to consider the nature of this transition state rather than merely to concentrate on the nature of the reactants. 

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