Rate of reaction The change in concentration

Rate of reaction The change in concentration of a reactant or product per unit time. 

The rate of reaction—the change in concentration of reactant (or product) per unit time—varies as the reaction proceeds it is fastest at the beginning of the reaction and slowest at the end. 

Optical cells are used to investigate phase equilibria at high pressures as well as for analytical purposes. A more sophisticated approach consists of monitoring the changes in concentration to determine the rate of chemical reactions. 

Rate constant the proportionality constant in the relationship between reaction rate and reactant concentrations. (15.2) Rate of decay the change in the number of radioactive nuclides in a sample per unit time. (21.2)... 

The area of chemistry concerned with the speed, or rate, at which a chemical reaction occurs is called chemical kinetics. The word kinetic suggests movement or change in Chapter 5 we defined kinetic energy as the energy available because of the motion of an object. Here kinetics refers to the rate of a reaction, or the reaction rate, which is the change in concentration of a reactant or a product with time (M/s). 

The value of the second-order rate constant for the ionic-reactant-catalyzed reaction of a reactive substrate should be large enough to exhibit a change in the reaction rate caused by the change in concentration of the reactive ionic reactant due to ion exchange. 

A final requirement for a chemical kinetic method of analysis is that it must be possible to monitor the reaction s progress by following the change in concentration for one of the reactants or products as a function of time. Which species is used is not important thus, in a quantitative analysis the rate can be measured by monitoring the analyte, a reagent reacting with the analyte, or a product. For example, the concentration of phosphate can be determined by monitoring its reaction with Mo(VI) to form 12-molybdophosphoric acid (12-MPA). 

Direct-Computation Rate Methods Rate methods for analyzing kinetic data are based on the differential form of the rate law. The rate of a reaction at time f, (rate)f, is determined from the slope of a curve showing the change in concentration for a reactant or product as a function of time (Figure 13.5). For a reaction that is first-order, or pseudo-first-order in analyte, the rate at time f is given as... 

The rate, or velocity, at which this reaction approaches its equilibrium position can be determined by following the change in concentration of a reactant or a product as a function of time. For example, if we monitor the concentration of reactant A, we express the rate as... 

Reaction quotient (Q) An expression with the same form as Kbut involving arbitrary rather than equilibrium partial pressures, 333-334 Reaction rate The ratio of the change in concentration of a species divided by the time interval over which the change occurs, 285 catalysis for, 305-307 collision model, 298-300 concentration and, 287-292,314q constant, 288 enzymes, 306-307 egression, 288... 

In the absence of added mineral acid, the effective chlorinating species was concluded to be chlorine acetate. Like the catalysed chlorination, the rate of chlorination (of toluene) falls rapidly on changing the solvent from anhydrous to 98 % aqueous acetic acid, passes through a shallow minimum and thence to a maximum in 50 % aqueous acid this was thus attributed to a combination of the decrease in concentration of chlorine acetate as water is added and a solvent effect. By correcting for the change in concentration of chlorine acetate in the different media it was shown that the reaction rate increases as the water content of the media increases. 

As found by the earlier workers451,454, reaction takes place upon the small amount of free base present since ortho, para-substitution occurs. Observed second-order rate coefficients increased with increasing ethanol content of the medium, being approximately twice as large for 85 vol. % ethanol as for 20 vol. %, and this was found to derive from the change in concentration of free base with ethanol content of the medium for when this change is allowed for, the rate coefficient for... 

The average rate of a reaction is the change in concentration of a species divided by the time over which the change takes place the unique average rate is the average rate divided by the stoichiometric coefficient of the species monitored. Spectroscopic techniques are widely used to study reaction rates, particularly for fast reactions. 

FIGURE 13.4 The rate ol reaction is the change in concentration of a reactant (or product) divided by the time interval over which the change occurs (the slope of the line AB, for instance). The instantaneous rate is the slope of the tangent to the curve at the time of interest. 

Patterns in reaction rate data can often be identified by examining the initial rate of reaction, the instantaneous rate of change in concentration of a species at the instant the reaction begins (Fig. 13.6). The advantage of examining the initial rate is that the products present later in the reaction may affect the rate the interpretation of the rate is then quite complicated. There are no products present at the start of the reaction, and so any pattern due to the reactants is easier to find. 

The average rate of a reaction can be expressed as the change in concentration (A c) over some time interval... 

On the left side of the rate law, the rate of reaction Is expressed In terms of changes in concentration and... 

A second way to simplify the behavior of a reaction is the method of initial rates. In this method, we measure the rate at the very beginning of the reaction for different concentrations. A set of experiments is done, changing only one initial concentration each time. Instead of measuring the concentration at many different times during the reaction, we make just one measurement for each set of concentrations. The reaction orders can be evaluated from the relationships between the changes in concentration and the changes in initial rates. We illustrate how this works using a gas-phase reaction of H2 with NO 2H2(g) -b 2NO(g) N2(g) + 2H2 0(g)... 

A chemical equation shows that as a chemical reaction takes place, reactants are changed into products. The reaction rate of a chemical reaction is often expressed as the change in concentration of a reactant or a product in a unit amount of time. In this activity, the reaction rate will be calculated from the amount of time it takes for a given amount of magnesium (Mg) to react completely with hydrochloric acid (HCI). 

To determine the rate behavior of chain growth polymerization reactions, we rely on standard chemical techniques. We can choose to follow the change in concentration of the reactive groups, such as the carboxylic acid or amine groups above, with spectroscopic or wet lab techniques. We may also choose to monitor the average molecular weight of the sample as a function of time. From these data it is possible to calculate the reaction rate, the rate constant, and the order of the reacting species. 

The rate of a reaction is defined as the change in concentration of any of its reactants or products per unit time. There are six factors that affect the rate of a reaction ... 

You cannot tell if the change in rate stems from the change in A concentration, the change in B concentration, or both. Keeping all but one of the factors constant during a series of reactions, and using the effect of that one change, is the characteristic of a controlled experiment. 

The temperature increases the rate of the one-stage simple reaction. The situation is different in the case of chain reaction. The change in temperature and other conditions not only change the reaction rate but can change the mechanism of the reaction and composition of the formed products. This can be illustrated by analysis of the mechanism of the hydrocarbon oxidation at different temperatures, concentration of the reactants, and the rates of initiation [288]. Varying the conditions of oxidation, the mechanism and products of the reaction can be changed. 

If one of the components for the bimolecular reaction is in excess (e.g. [H] > [G]) and the changes in concentrations due to the perturbation are small, the kinetics follow an exponential function where the observed rate constant (kohs) is given by... 

The rate of reaction is the change in concentration per change in time. It is possible to find the rate of reaction from a graph of concentration of a reactant versus time. The procedure involves drawing a tangent to the curve at the point in the reaction where we wish to know the rate. 

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