Factors that affect the rate of a reaction

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 ... 

Most of the factors that affect the rate of a reaction are qualitative or semiquantitative, but the dependency of the rate on concentration (or pressure, which is a measure of concentration) may be... 

The idea of equilibrium hinges on the concept of reaction rates. In chemistry rate refers to how much something changes in a unit of time. The something that changes is the concentration of a reactant or a product, usually expressed as molarity. The unit of time is generally the second, although any unit of time can be used. Sometimes it is desirable to manipulate the rate of a reaction in order to speed it up or slow it down. The factors that affect the rate of a reaction are temperature, concentration, surface area, and the use of a catalyst. 

Up to this point, we have primarily studied the descriptive aspects of chemical reactions. That is, we ve discussed what s occurring during reactions without much detail about the driving forces behind the reactions. The purpose of the next two chapters is to provide such detail. In this chapter, we will look at the major models that have been developed to explain the mechanisms by which reactions occur. The focus of this chapter is kinetics, an area of chemistry that explores the rates at which chemical reactions occur. In the first portion of the chapter, we will focus on a few techniques we use to describe or define the rate of a reaction. Once that is established, we will move our attention to the factors that affect the rate of a reaction concentration, temperature, surface area, and the presence of a catalyst. 

Because chemical equilibrium involves rates of reactions, this chapter first investigates the factors that affect the rate of a reaction (Section 18.1). The molecular basis of chemical equilibrium and some of its terminology are then presented in Section 18.2. LeChatelier s principle, discussed in Section 18.3, explains qualitatively how to predict what happens to a system at equilibrium when a change is imposed on the system. Section 18.4 presents the equilibrium constant, which allows us to obtain quantitative results for systems at equilibrium. 

Describe exothermic and endothermic reactions and factors that affect the rate of a reaction. 

However, some sets of reactants can undergo both a forward and a reverse reaction under the same set of conditions. This circumstance leads to a state called chemical equilibrium. Before we take up equilibrium, however, we have to learn about the factors that affect the rate of a chemical reaction. 

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. 

The rates of all of these radical reactions are affected by the same factors that affect the rates of other reactions. More stable radicals are formed more readily, react more slowly, and have longer lifetimes. In addition, steric hindrance can prevent two radicals from approaching close enough to couple, thus increasing the lifetime of the radical. As an example of the importance of steric factors, the 2,4,6-tri-terf-butylphenoxy radical does not couple in solution and can actually be isolated as a solid. 

Two major factors that affect the rate of a chemical reaction—the kinetics of the reaction—are concentration and temperature. The effects of both are easily demonstrated using items from our Shopping List and Solutions. ... 

An important factor that affects the rate of a chemical reaction is the reactive nature of the reactants. As you know, some substances react more readily than others. For example, calcium and sodium are both reactive metals however, what happens when each metal is added to water is distinctly different. When a small piece of calcium is placed in cold water, as shown in Figure 17-7a, the calcium and water react slowly to form hydrogen gas and aqueous calcium hydroxide. 

Another factor that affects the rate of a displacement reaction is the solubility of the nucleophile. Tetraalkylammonium salts have been used to increase the concentration of nucleophile for displacements at... 

We can control four factors that affect the rate of a given reaction the concentrations of the reactants, the physical state of the reactants, the temperature at which the reaction occurs, and the use of a catalyst. We ll consider the first three factors here and discuss the fourth later in the chapter. 

There are many factors that determine the rate of a reaction sequence that lead to a particular product. Within the same catalytic system, reaction sequences leading to different products may compete. The two key parameters, which are important to the selectivity of a catalytic reaction, are the difference of the rate constants of elementary reaction steps controlled by electronic, geometric or steric parameters and the overlayer composition of the reactive catalytic surface or occupancy of complex or cavity. This affects the relative probability for product molecule formation from the recombination or dissociation of reaction intermediates generated during the catalytic cycle. The relative stability of the fragment molecules determines their concentration and, hence the probability that they are present at high enough concentration to result in a finite quantity for recombination. Site occupancy controls also the probability of surface vacancies necessary for dissociation. The last, for instance, is an important parameter that discriminates between associative... 

Reaction rates are influenced by a nnmber of different factors. Four factors that affect the rates of all reactions are ... 

If molecules react via high-energy collisions, then the factors that influence the rate of a reaction must be the same factors that affect the number of high-energy collisions that occur per unit time. Here, we focus on the two most important factors the concentration of the reacting molecules and the temperature of the reaction mixture. 

The Five Factors that Affect the Rate of a Chemical Reaction... 

A catalyst is a substance that increases the rate of a reaction without affecting the position of equilibrium. It follows that the rate in the reverse direction must be increased by the same factor as that in the forward direction. This is a consequence of the principle of microscopic reversibility (Section 3.3), which applies at equilibrium, and rates are often studied far from equilibrium. 

Thus, factors that affect the rate of corrosion are essentially pH, partial pressure of oxygen, and solution conductivity there are also other less general factors that will be specified in the following sections. The half-reactions have to occur at different sites on the interface in order to form an electrical circuit, and thence the importance of solution conductivity. In particular cases other cathodic reactions can take place due to, for example, reduction of a species already present in solution such as Fe3+ reduced to Fe2+. 

The equilibrium constant expression is in the same form as the ratio in the Nemst equation (Chapter 17). The square brackets mean the molarity of the substance they enclose, and the constant K is called the equilibrium constant. The entire equation is known as the equilibrium constant expression. No matter what the initial concentrations of reactants or products, the ratio of the concentrations at equilibrium will be equal to the constant K. The value of K depends only on the specific chemical equation and on the temperature. It does not depend on any of the other factors that can affect the rate of a reaction. For example, if different quantities of the same reactants and products are introduced into different reaction vessels, they will react with one another until, at equilibrium, the same ratio of concentrations, each raised to the appropriate power, is established. 

The factors that affect the rate of the reaction are easily predictable, namely ones that are similar to those that affect the rate of an SN1 reaction. However, the stereochemical consequences of this pathway are slightly more difficult to predict. The simple carbanion would be expected to adopt a tetrahedral conformation, which is similar to that which a nitrogen atom adopts in a tertiary amine. Consider whether tertiary amines may be resolved into their enantiomers, and then by analogy, suggest what would be the stereochemical consequences of the SE1 mechanism on the configuration at the substituted centre. Hence, suggest what would be the structure of a simple carbanion intermediate. 

When all of the factors that affect the rate of the reaction (except concentration) are held constant (i.e., the nature of the reactant, temperature and physical state of the reactant, and the presence or absence of a catalyst) the rate of the reaction is proportional to the concentration of N2O5. 

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