Numerical Importance of the Equilibrium Expression

Being able to write an expression relating equilibrium concentrations in chemical reactions provides a powerful tool for understanding chemical equilibrium. We will soon see how to evaluate these expressions for several classes of reactions. But first, let s look at what we can learn from the numerical values of equilibrium constants. For example, we could ask the question, Which reaction is more likely to produce hydrogen gas at relatively low temperature—the BMA process or the Fluohmic process How can we use the equilibrium constants for these reactions to find the answer  

Equilibrium constants range over many orders of magnitude. Values as small as 10 are known, as are values as high as 10 or greater. What does the size of the equilibrium constant tell us about the reaction If we look at the equilibrium expression for a reaction as an algebraic relationship, the answer will become apparent. 

Concentrations of products are in the numerator, and concentrations of reactants are in the denominator. For a very large value of K, the product concentrations must be large and the reactant concentrations must he small. By contrast, for the value of K to be small, concentrations of the reactants must be large and those of products must be small. 

the value of K can tell us the direction in which a chemical reaction is likely to proceed. For large values of K, products are favored, whereas small values of K (meaning K 1) mean that at equilibrium most of the reactants will remain intact. If K is on the order of one, the equilibrium has significant concentrations of both reactants and products. Example Problem 12.3 provides some practice in interpreting the values of equilibrium constants. 

In Example Problem 12.2, we saw that cyanide ions precipitate with silver. Bromide ions show similar behavior. The two pertinent equilibria are 

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The Equilibrium (Mass Action) Expression Gas Phase Equilibria Kp vs. Kp Homogeneous and Heterogeneous Equilibria Numerical Importance of the Equilibrium Expression Mathematical Manipulation of Equilibrium Constants Reversing the Chemical Equation Adjusting the Stoichiometry of the Chemical Reaction Equilibrium Constants for a Series of Reactions Units and the Equilibrium Constant... 

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