Factors That Affect Chemical Equilibrium

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. 

Summary We ve been discussing chemical reactions for several chapters. In the Kinetics chapter you saw how chemical reactions take place and some of the factors that affect the reaction s speed. In this chapter we will discuss another aspect of chemical reactions equilibrium. 

Eventually, the current catalysis science usually leave behind serious numerous physicochemical factors that affect the composition and size of particles of a heterogeneous catalyst at the stage of its preparation, even though the catalyst preparation often comprises hydrothermal processes that were well understood in equilibrium thermodynamics of geochemical processes. Even thermodynamic factors such as those that affect the surface state of the operating catalyst, its chemical composition, and potential sur face reconstruction under the action of the reaction medium are not well understood. AH of these include the phenomena that control the most important properties of the catalyst in the course of the reaction it catalyzes. 

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. 

Next, it is necessary to identify the dominating factors that affect the chemical reactions and select the most suitable reactor configuration. For homogeneous chemical reactions, one of three factors often dominates (i) equilibrium limitation of the desirable reaction, (ii) the formation of undesirable products (by side reactions), and (iii) the amount of heat that should be transferred. For example, if a low concentration of the reactants suppresses the formation of the undesirable product, a CSTR is preferred over a tubular reactor even though a larger reactor... 

Knowing the factors that affect chemical equilibrium has great practical value for industrial applications, such as the synthesis of ammonia. The Haber process for synthesizing ammonia from molecular hydrogen and nitrogen uses a heterogeneous catalyst to speed up the reaction (see p. 540). Let us look at the equilibrium reaction for ammonia synthesis to determine whether there are factors that could be manipulated to enhance the yield. 

To understand why and how chemical reactions happen it is necessary to consider also intermolecular interactions. It is only in the hypothetical case of an ideal gas that intermolecular interactions are totally absent. In all other systems they represent an important factor that affects molecular conformation, reactivity and stability. Whenever molecules co-exist in equilibrium it means that intermolecular forces are not sufficient to pull the molecules apart or together into larger aggregates. Equilibrium implies a balance of thermodynamic factors, and when these factors change, intermolecular interactions may overcome the integrity of a partially holistic molecule, and lead on to chemical reaction. Onset of the reaction is said to be controlled by an activation energy barrier. This barrier must clearly be closely allied to the quanmm potential of the molecule. 

Factors That Affect Chemical Equilibrium Changes in concentration can affect the position of an equilibrium state—that is, the relative amounts of reactants and products. Changes in pressure and volume may have the same effect for gaseous systems at equilibrium. Only a change in temperature can alter the value of equilibrium constant. A catalyst can establish the equilibrium state faster by speeding the forward and reverse reactions, but it can change neither the equilibrium position nor the equilibrium constant. 

SECTION 1S.S Factors That Affect Chemical Equilibrium... 

---