15-4 The Significance of the Magnitude of the Equilibrium Constant.

1. 15-4 The Significance of the Magnitude of the Equilibrium Constant.

2. [G]tg[H]th Qc = [A]tm[B]tn 15-5 The Reaction Quotient, Q: Predicting the Direction of Net Change. • Equilibrium can be approached various ways. • Qualitative determination of change of initial conditions as equilibrium is approached is needed. k1 CO(g) + 2 H2(g) CH3OH(g) k-1 At equilibrium Qc = Kc

3. Reaction Quotient

4. 15-6 Altering Equilibrium Conditions: Le Châtelier’s Principle • When an equilibrium system is subjected to a change in temperature, pressure, or concentration of a reacting species, the system responds by attaining a new equilibrium that partially offsets the impact of the change. What happens if we add SO3 to this equilibrium?

5. k1 2 SO2(g) + O2(g) 2 SO3(g) k-1 [SO3]2 Q = = Kc [SO2]2[O2] Le Châtelier’s Principle Kc = 2.8102 at 1000K Q > Kc

6. nSO3 2 2 nSO3 V [SO3] = = V Kc = nSO2 nO2 2 nSO2 nO2 2 [SO2]2[O2] V V Effect of Condition Changes • Adding a gaseous reactant or product changes Pgas. • Adding an inert gas changes the total pressure. • Relative partial pressures are unchanged. • Changing the volume of the system causes a change in the equilibrium position.

7. nG nH g h V-Δn = nA nB a a Effect of Change in Volume [G]g[H]h nG nH g h Kc = = V(a+b)-(g+h) • When the volume of an equilibrium mixture of gases is reduced, a net change occurs in the direction that produces fewer moles of gas. When the volume is increased, a net change occurs in the direction that produces moremoles of gas. [C]c[D]d nA nB a a

8. Effect of the Change of Volume ntot = 1.16 mol gas 1.085 mol gas 415 KP = 338

9. Effect of Temperature on Equilibrium • Raisingthe temperature of an equilibrium mixture shifts the equilibrium condition in the direction of theendothermic reaction. • Loweringthe temperature causes a shift in the direction of theexothermicreaction.

10. Effect of a Catalyst on Equilibrium • A catalyst changes the mechanism of a reaction to one with a lower activation energy. • A catalyst has no effect on the condition of equilibrium. • But does affect the rate at which equilibrium is attained.

11. 15-7 Equilibrium Calculations: Some Illustrative Examples. • Numerical examples are given in the text that illustrate ideas that have been presented in this chapter. • Refer to the “comments” which describe the methodology. These will help in subsequent chapters. • Exercise your understanding by working through the examples with a pencil and paper.