NOTES 15-4 Obj 15.7

© 2009, Prentice- Hall, Inc Le Châtelier’s Principle A.) “If a system at equilibrium is disturbed by a change in temperature, pressure, or the concentration of one of the components, the system will shift its equilibrium position so as to counteract the effect of the disturbance.”

B.) The Haber Process :The transformation of nitrogen and hydrogen into ammonia (NH 3 ) is of tremendous significance in agriculture, where ammonia-based fertilizers are of utmost importance.

© 2009, Prentice-Hall, Inc. 1.) If H 2 is added to the system, N 2 will be consumed and the two reagents will form more NH 3.

2.) This apparatus helps push the equilibrium to the right by removing the ammonia (NH 3 ) from the system as a liquid.

Figure 15.13

© 2009, Prentice- Hall, Inc. C.) The Effect of Changes in Temperature Co(H 2 O) 6 2+ (aq) + 4 Cl (aq) CoCl 4 (aq) + 6 H 2 O (l)

Sample Exercise Using Le Châtelier’s Principal to Predict shifts in Equilibrium Consider the equilibrium In which direction will the equilibrium shift when (a) N 2 O 4 is added, (b) NO 2 is removed, (c) the total pressure is increased by addition of N 2 (g), (d) the volume is increased, (e) the temperature is decreased?

Sample Exercise Using Le Châtelier’s Principal to Predict shifts in Equilibrium For the reaction in which direction will the equilibrium shift when (a) Cl 2 (g) is removed, (b) the temperature is decreased, (c) the volume of the reaction system is increased, (d) PCl 3 (g) is added? Practice Exercise

Sample Exercise Predicting the Effect of Temperature on K (a) Using the standard heat of formation data in Appendix C, determine the standard enthalpy change for the reaction (b) Determine how the equilibrium constant for this reaction should change with temperature.

Using the thermodynamic data in Appendix C, determine the enthalpy change for the reaction Use this result to determine how the equilibrium constant for the reaction should change with temperature. Practice Exercise

D.) Catalysts increase the rate of both the forward and reverse reactions.

E.) When one uses a catalyst, equilibrium is achieved faster, but the equilibrium composition remains unaltered.

Sample Integrative Exercise Putting Concepts Together At temperatures near 800 °C, steam passed over hot coke (a form of carbon obtained from coal) reacts to form CO and H 2 : The mixture of gases that results is an important industrial fuel called water gas. (a) At 800 °C the equilibrium constant for this reaction is K p = What are the equilibrium partial pressures of H 2 O, CO, and H 2 in the equilibrium mixture at this temperature if we start with solid carbon and mol of H 2 O in a 1.00-L vessel? (b) What is the minimum amount of carbon required to achieve equilibrium under these conditions? (c) What is the total pressure in the vessel at equilibrium? (d) At 25°C the value of K p for this reaction is 1.7 × 10 –21. Is the reaction exothermic or endothermic? (e) To produce the maximum amount of CO and H 2 at equilibrium, should the pressure of the system be increased or decreased?