Equilibrium expressions heterogeneous equilibria

Equilibrium Expressions Heterogeneous Equilibria Manipulating Equilibrium Expressions... 

Words that can be used as topics in essays 5% rale buffer common ion effect equilibrium expression equivalence point Henderson-Hasselbalch equation heterogeneous equilibria homogeneous equilibria indicator ion product, P Ka Kb Kc Keq KP Ksp Kw law of mass action Le Chatelier s principle limiting reactant method of successive approximation net ionic equation percent dissociation pH P Ka P Kb pOH reaction quotient, Q reciprocal rule rule of multiple equilibria solubility spectator ions strong acid strong base van t Hoff equation weak acid weak base... 

The following Sample Problem shows how to find the equilibrium expression for a reaction. In this chapter, you will use equilibrium expressions for homogeneous reactions (mostly reactions between gases). In Chapters 8 and 9, you will learn how to use equilibrium expressions for heterogeneous systems. 

The binding equilibrium expressed as shown above (2.2) is actually a gross oversimplification of the situation. The heterogeneity of the binding sites and multiple valency of individual antibodies lead to formation of secondary bonds that contribute to hysteresis or ripening of the antibody-antigen complex. Its ultimate form is the polymerization of a primary complex, which happens when the antigen is also polyvalent. Formation of the polymer (precipitin reaction) renders such a reaction virtually irreversible. 

For a heterogeneous equilibrium (a chemical equilibrium with components in different phases), reactants or products may be pure liquids or solids. The concentration of a pure liquid or solid in moles/liter cannot change. It is a constant property of the material, and these constants are incorporated into the equilibrium constant. Therefore the concentrations of pure liquids and solids are absent from equilibrium expressions for heterogeneous equilibria. 

This equilibrium is known as a heterogeneous equilibrium, which is to say that it consists of substances that are in different states (phases). If you recall from Chapter 13, the equilibrium constant expressions for such equilibria do not contain the concentrations of liquids or solids. The equilibrium expression for this reaction will describe the degree to which the solid dissolves in solution, which is another way to say the degree to which it is soluble. And since the solid is not shown in the equilibrium expression, the equilibrium constant will express the product of the concentrations of the dissolved solute ions. For this reason, the equilibrium constant is referred to as the solubility-product constant. For this equilibrium, the solubility-product constant, Ksp is ... 

One cannot tell by looking at an expression such as equation 1, however, whether the overall balanced equation applies to a homogeneous equilibrium, or to a heterogeneous equilibrium in which has been included a second equilibrium, perhaps associated with and dependent upon the first. If we assume homogeneous equilibrium for equation 1, and include with each cation to avoid the necessity of a separate H" " variable, then... 

However, experimental results show that the position of a heterogeneous equilibrium does not depend on the amounts of pure solids or liquids present (see Fig. 6.6). This result makes sense when the meaning of an activity for a pure liquid or solid is understood. For a pure liquid or solid the reference state is the pure liquid or solid. Thus, for the composition of CaC03 considered above, we do not insert [CaC03] or [CaO] into the equilibrium expression but rather into the activity of each ... 

The quantitative relations involved in heterogeneous solid-solution formation were considered by Doerner and Hoskins, who derived the equilibrium expression. For silver bromide and chloride the two extreme situations are represented by... 

It is believed that the Kp data for the three homogeneous reactions (A, B, and C) are more reliable than those for the heterogeneous reaction (D) due to the need for a machine calibration constant which appears in the equilibrium expression for the latter. Ehlert et al. (2) determined this constant from vaporization experiments performed with silver contained in their Knudsen cell. Further support for this belief is provided by the large positive drift that arises in the 3rd law analysis of these Kp s. Also, it Is felt that the results otained from the flame-spectrophotometric studies (4, are somewhat more... 

Constants for heterogeneous equilibria You have learned to write expressions for homogeneous equilibria, those in which all reactants and products are in the same physical state. When the reactants and products of a reaction are present in more than one physical state, the equilibrium is called a heterogeneous equilibrium. 

You are given a heterogeneous equilibrium involving gases and solids. The general form of the equilibrium constant expression for this reaction is... 

For more practice writing heterogeneous equilibrium constant expressions, go to Supplemental Practice Problems in Appendix A. 

Heterogeneous Equilibrium). Hence, the concentration of the solid is not included in the equilibrium constant expression. For a saturated solution of BaSO in contact with solid BaSO, we write... 

A chemical equilibrium process in which all reactants and products are in the same phase is homogeneous. If the reactants and products are not all in the same phase, the equilibrium is heterogeneous. The concentrations of pure solids, pure liquids, and solvents are constant and do not appear in the equilibrium constant expression of a reaction. 

For the heterogeneous reactions, there are no terms for the solid phases in the equilibrium expressions, and this can be easily shown to be the case experimentally. Altering the amount of solid present has no effect on the constancy of these quantities at equilibrium. Again that this is so can be demonstrated conclusively by the thermodynamic derivation of the algebraic form of the equilibrium relations (see Section 8.14). 

Therefore the concentrations of pure liquids and solids are absent from equilibrium expressions for heterogeneous equilibria. 

Law of chemical equilibrium Equilibrium expression Equilibrium constant Equilibrium position Homogeneous equilibria Heterogeneous equilibria... 

Write the equilibrium expression for each of the following heterogeneous equilibria. 

In a heterogeneous equilibrium a solid substance does not appear in the expression for K. ... 

A simplification occurs with heterogeneous equilibria because the concentrations of pure solids and pure liquids are constant at a fixed temperature (see page 137). For example, the equilibrium expression for the production of carbon monoxide from coke and carbon dioxide,... 

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