Equilibrium expression for heterogeneous equilibria

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. 

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

Writing equilibrium expressions for heterogeneous equilibria is also straightforward, but it is slightly different from what we have done so far for homogeneous equilibria. For example, carbon dioxide can combine with elemental carbon to produce carbon monoxide ... 

Think About It Like writing equilibrium expressions for homogeneous equilibria, writing equilibrium expressions for heterogeneous equilibria becomes second nature if you practice. The importance of developing this skill now cannot be overstated. Your ability to tmderstand the principles and to solve many of the problems in this and Chapters 16 to 19 depends on your ability to write equilibrium expressions correctly and easily. 

Example 16.3 Writing Equilibrium Expressions for Heterogeneous Equilibria... 

Explain why pure solids and liquids are left out of equilibrium constant expressions for heterogeneous equilibria. 

Expressions for heterogeneous equilibria You have learned to write Keq expressions for homogeneous equilibria, those in which all reactants and products are in the same physical state. When the reactants and products are present in more than one physical state, the equilibrium is called a heterogeneous equilibrium. When ethanol is placed in a closed flask, a liquid-vapor equilibrium is established, as illustrated in Figure 17.8. 

As with any equilibrium, the extent to which this dissolution reaction occurs is expressed by the magnitude of its equilibrium constant. Because fliis equilibrium equation describes the dissolution of a solid, the equilibrium constant indicates how soluble tire solid is in water and is referred to as the solubility-product constant (or simply tire solubility product). It is denoted Kgp, where sp stands for solubility product. The equilibrium-constant expression for this process is written according to tire same rules as those that apply to any equilibrium-constant expression. That is, Ihe concentration terms of the products are multiplied togefli-er, and each is raised to the power of its stoichiometric coefficient in the balanced chemical equation, and these are divided by the concentration terms of the reactants multiplied together, and each raised to the power of its stoichiometric coefficient. Solids, liquids, and solvents do not appear in the equilibrium-constant expressions for heterogeneous equilibria (Section 15.3), however, so the solubility product equals the product of the concentration (f the ions involved in the equilibrium, each raised to the poioercfits coefficient in the equilibrium equation. Thus, the solubility-product expression for the equilibrium expressed in Equation 17.15 is... 

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 ... 

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

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,... 

HETEROGENEOUS EQUILIBRIA We learn how to write equilibrium-constant expressions for heterogeneous reactions. 

Analyze We are given three chemical equations, all for heterogeneous equilibria, and are asked to write the corresponding equilibrium-constant expressions. 

S.S Heterogeneous Equilibria The Equilibrium Expression for Reactions Involving a Solid or a Liquid ... 

Write equilibrium constant expressions for these heterogeneous equilibria. 

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