Factors affecting reaction rate reactant concentration

In the previous chapter, we discussed the rate of reactions and the factors affecting reaction rates. We also learned that there is a relation between the concentration of reactants and the rate. 

In Lab 17.1, you learned about the effect of temperature and concentration on reaction rate. Another factor that affects reaction rate is the amount of surface area of the reactants. If a chemical reaction is to take place, the molecules of reactants must collide. Changing the amount of surface area modifies the rate of collision, and, thus, the rate of reaction. If surface area increases, collision frequency increases. If surface area decreases, so does the number of collisions. In this lab, you will examine the effect of surface area on rate of reaction. You will also determine how a combination of factors can affect reaction rate. 

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. 

You can use simple collision theory to begin to understand why factors such as concentration affect reaction rate. If a collision is necessary for a reaction to occur, then it makes sense that the rate of the reaction will increase if there are more collisions per unit time. More reactant particles in a given volume (that is, greater concentration) will increase the number of collisions between the particles per second. Figure 6.7 illustrates this idea. 

Another factor that affects the rate of a chemical reaction is the concentration of reactants. As noted, most reactions take place in solutions. It is expected that as the concentration of reactants increases more collisions occur. Therefore, increasing the concentrations of one or more reactants generally leads to an increase in reaction rate. The dependence of reaction rate on concentration of a reactant is determined experimentally. A series of experiments is usually conducted in which the concentration of one reactant is changed while the other reactant is held constant. By noting how fast the reaction takes place with different concentrations of a reactant, it is often possible to derive an expression relating reaction rate to concentration. This expression is known as the rate law for the reaction. 

We explore four variables that affect reaction rates concentration, physical states of reactants, temperature, and presence of catalysts. These factors can be understood in terms of the collisions among reactant molecules that lead to reaction. 

Four factors affect the rates of all reactions (1) the nature of the reactants, (2) reactant concentrations, (3) reactant temperature, and (4) the presence of catalysts. 

The Rate ofa Reaction Factors That Affect Reaction Rates 16-2 Nature of the Reactants 16-3 Concentrations of Reactants ... 

The rate of a reaction is generally affected by all or some of the following factors temperature, reaction medium, the concentration of reactants and cata-... 

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 ... 

The rate of an exothermic chemical reaction determines the rate of energy release, so factors which affect reaction kinetics are important in relation to possible reaction hazards. The effects of proportions and concentrations of reactants upon reaction rate are governed by the Law of Mass Action, and there are many examples where changes in proportion and/or concentration of reagents have transformed an... 

The five factors that can affect the rates of chemical reaction are the nature of the reactants, the temperature, the concentration of the reactants, the physical state of the reactants, and the presence of a catalyst. 

How do factors such as concentration, temperature, a different reactant, and surface area affect the rate of this reaction ... 

In this section, you learned how to relate the rate of a chemical reaction to the concentrations of the reactants using the rate law. You classified reactions based on their reaction order. You determined the rate law equation from empirical data. Then you learned about the half-life of a first-order reaction. As you worked through sections 6.1 and 6.2, you may have wondered why factors such as concentration and temperature affect the rates of chemical reactions. In the following section, you will learn about some theories that have been developed to explain the effects of these factors. 

In Equation 3.1, the suffix i usually designates a reaction product. Ihe rate r,-is negative, in case i is a reactant. Several factors, such as temperature, pressure, the concentrations of the reactants, and also the existence of a catalyst affect the rate of a chemical reaction. In some cases, what appears to be one reaction may in fact involve several reaction steps in series or in parallel, one of which may be rate limiting. 

Table 10.5 provides performance data regarding the SCWO process. Typical destruction efficiencies (DEs) for a number of compounds are also summarized in Table 10.5, which indicates that the DE could be affected by various parameters such as temperature, pressure, reaction time, oxidant type, and feed concentration. Feed concentrations can slightly increase the DE in supercritical oxidation processes. For SCWO, the oxidation rates appear to be first order and zero order with respect to the reactant and oxygen concentration, respectively. Depending upon reaction conditions and reactants involved, the rate of oxidation varies considerably. Pressure is another factor that can affect the oxidation rate in supercritical water. At a given temperature, pressure variations directly affect the properties of water, and in turn change the reactant concentrations. Furthermore, the properties of water are strong functions of temperature and pressure near its critical point. 

Complexity in multiphase processes arises predominantly from the coupling of chemical reaction rates to mass transfer rates. Only in special circumstances does the overall reaction rate bear a simple relationship to the limiting chemical reaction rate. Thus, for studies of the chemical reaction mechanism, for which true chemical rates are required allied to known reactant concentrations at the reaction site, the study technique must properly differentiate the mass transfer and chemical reaction components of the overall rate. The coupling can be influenced by several physical factors, and may differently affect the desired process and undesired competing processes. Process selectivities, which are determined by relative chemical reaction rates (see Chapter 2), can thenbe modulated by the physical characteristics of the reaction system. These physical characteristics can be equilibrium related, in particular to reactant and product solubilities or distribution coefficients, or maybe related to the mass transfer properties imposed on the reaction by the flow properties of the system. 

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