Dynamic Equilibrium and the Equilibrium Constant 14.2-14.3 Dynamic Equilibrium and the Equilibrium Constant

Dynamic Equilibrium State in which rate of forward reaction = rate of reverse reaction Concentrations of reactants & products are fixed Not inherently equal Reaction continues to occur, just at constant rate

Equilibrium Constant Ratio of concentrations of products raised to their stoichiometric coefficients, divided by concentration of reactants raised to their stoichiometric coefficients Used to quantify concentration of reactants and products at dynamic equilibrium Uses denotation K Non-italicized K for Kelvins aA + bB cC + dD

Law of Mass of Actions How to figure out equilibrium constant [C]c[D]d K= ------------ [A]a[B]b Does not indicate speed of reaction, only how far along reaction is when it hits dynamic equilibrium aA + bB cC + dD

Practice 2NO2 ⇌ N2O4 H2SO4 ⇌ 2 H+ + SO42-

Significance of Equilibrium Constant K < 1 : reverse reaction is favored, forward reaction does not go very far K = 1 : neither direction is favored, forward reaction goes about halfway K > 1 : forward reaction is favored, forward reaction proceeds essentially to completion

Relationship Between Equilibrium Constant and Chemical Equation 1. If equation is reversed, invert constant Kreverse = 1/ Kforward = K’ 2. If coefficients are multiplied by a common factor, raise equilibrium constant to same factor 3. If adding two or more individual chemical equations, multiply corresponding equilibrium constants by each other to obtain one equilibrium constant

Practice Consider following chemical reaction and equilibrium constant at 25 degrees C 2COF2(g) CO2(g) + CF4(g) K = 2.2 x 106 Calculate equilibrium constant for following reaction at 25 degrees C 2CO2(g) + 2CF4(g) 4COF2(g) K’ = ?

Practice Consider chemical equation and equilibrium constant for synthesis of ammonia at 25 degrees C N2(g) + 3H2(g) 2NH3(g) K = 5.6 x 105 Calculate equilibrium constant for following reaction at 25 degrees C NH3(g) 1/2 N2(g) + 3/2 H2(g) K’ = ?