Chapter 13 Lecture Basic Chemistry Fourth Edition Chapter

Chapter 13 Lecture Basic Chemistry Fourth Edition Chapter 13 Reaction Rates and Chemical Equilibrium 13. 5 Changing Equilibrium Conditions: Le Châtelier’s Principle Learning Goal Use Le Châtelier’s Principle to describe the changes made in equilibrium concentrations when the reaction conditions change. Hypoxia may occur at high altitudes where the oxygen concentration is lower. © 2014 Pearson Education, Inc.

Le Châtelier’s Principle When the conditions of a reaction at equilibrium are changed, the forward and reverse reactions will no longer be equal. Le Châtelier’s Principle states that when a stress (change in conditions) is placed on a reaction at equilibrium, the equilibrium will shift in a direction that relieves the stress. © 2014 Pearson Education, Inc.

Le Châtelier’s Principle When water is added to one tank, the levels readjust to equalize. © 2014 Pearson Education, Inc.

Changing Equilibrium, Adding Reactant Consider the following reaction at equilibrium: Adding reactant H 2(g) + I 2(g) 2 HI(g) If more reactant (H 2 or I 2) is added, • the rate of the forward reaction increases to form more product until the system is again at equilibrium • the effect of adding reactant shifts the equilibrium toward the products © 2014 Pearson Education, Inc.

Changing Equilibrium, Adding Reactant (a) The addition of H 2 places stress on the equilibrium system of H 2(g) + I 2(g) 2 HI(g). (b) To relieve the stress, the forward reaction converts some reactants H 2 and I 2 to product HI. (c) A new equilibrium is established when the rates of the forward reaction and the reverse reaction become equal. © 2014 Pearson Education, Inc.

Changing Equilibrium, Removing Reactant Consider the following reaction at equilibrium: Removing reactant H 2(g) + I 2(g) 2 HI(g) If a reactant (H 2 or I 2) is removed, • the rate of the reverse reaction increases to form more reactant until the equilibrium is reached • the effect of removing a reactant shifts the equilibrium toward the reactants © 2014 Pearson Education, Inc.

Changing Equilibrium, Adding Product Consider the following reaction at equilibrium: Adding product H 2(g) + I 2(g) 2 HI(g) If more HI is added, • the rate of the reverse reaction increases to form more H 2 and I 2 reactants • the effect of adding a product shifts the equilibrium toward the reactants © 2014 Pearson Education, Inc.

Changing Equilibrium, Removing Product Consider the following reaction at equilibrium: Removing product H 2(g) + I 2(g) 2 HI(g) When product (HI) is removed, • there is a decrease in collisions of HI molecules • the rate of the forward reaction increases and forms more products, HI © 2014 Pearson Education, Inc.

Effect of Concentration Changes on Equilibrium © 2014 Pearson Education, Inc.

Effect of a Catalyst on Equilibrium • Adding a catalyst speeds up a reaction by lowering the activation energy, increasing the rate of the forward and reverse reactions. • The time to reach equilibrium is shorter; however, the same ratios of reactants and products are present. • The addition of a catalyst does not change the equilibrium mixture. © 2014 Pearson Education, Inc.

Effect of Decreasing Volume on Equilibrium A change in the volume of a gas mixture at equilibrium will change the concentration of the gases in the mixture. Decreasing volume, shifts toward fewer moles 2 CO(g) + O 2(g) 2 CO 2(g) Decreasing the volume increases the concentration of the gases. The system shifts in the direction of the smaller number of moles to compensate. © 2014 Pearson Education, Inc.

Effect of Increasing Volume on Equilibrium A change in the volume of a gas mixture at equilibrium will change the concentration of the gases in the mixture. Increasing volume, shifts toward more moles 2 CO(g) + O 2(g) 2 CO 2(g) Increasing the volume decreases the concentration of the gases. The system shifts in the direction of the larger number of moles to compensate. © 2014 Pearson Education, Inc.

Volume Changes, Equilibrium (a) A decrease in the volume of the container causes the system to shift in the direction of fewer moles of gas. (b) An increase in the volume of the container causes the system to shift in the direction of more moles of gas. © 2014 Pearson Education, Inc.

Chemistry Link to Health, Hb Oxygen transport involves an equilibrium between hemoglobin (Hb), oxygen, and oxyhemoglobin (Hb. O 2). Hb(aq) + O 2(g) Hb. O 2(aq) • When there is a high concentration of O 2 in the alveoli of the lungs, the reaction shifts to make more oxyhemoglobin. • When the concentration of O 2 is low in the tissues, the reverse reaction releases O 2 from oxyhemoglobin. © 2014 Pearson Education, Inc.

Chemistry Link to Health, Hb Given the reaction of hemoglobin: Hb(aq) + O 2(g) Hb. O 2(aq) • At normal atmospheric pressure, oxygen diffuses into the blood because the partial pressure of oxygen in the alveoli is higher than that in the blood. • At altitudes above 8000 ft, a decrease in atmospheric pressure results in a lower pressure of O 2. © 2014 Pearson Education, Inc.

Chemistry Link to Health, Hb At an altitude of 18, 000 ft, a person will obtain 29% less oxygen and may experience hypoxia. Hypoxia may occur at high altitudes where the oxygen concentration is lower. © 2014 Pearson Education, Inc.

Chemistry Link to Health, Hb According to Le Châtelier’s Principle, a decrease in oxygen • shifts the equilibrium in the direction of the reactants • depletes the concentration of Hb. O 2, causing hypoxia Removing reactant Hb(aq) + O 2(g) © 2014 Pearson Education, Inc. Hb. O 2 (aq)

Endothermic Reaction Equilibrium and Temperature Decreasing the temperature of an endothermic reaction • causes the system to respond by shifting the reaction toward more heat • shifts the reaction toward the reactants, increasing heat in the system Decrease temperature N 2(g) + O 2(g) + heat © 2014 Pearson Education, Inc. 2 NO(g)

Endothermic Reaction Equilibrium and Temperature Increasing the temperature of an endothermic reaction • causes the system to respond by shifting the reaction to remove heat • shifts the reaction toward the products, using up the heat Increase temperature H 2(g) + O 2(g) + heat © 2014 Pearson Education, Inc. 2 NO(g)

Exothermic Reaction Equilibrium and Temperature Decreasing the temperature of an exothermic reaction • causes the system to respond by shifting the reaction toward more heat • shifts the reaction toward the products, increasing heat in the system Decrease temperature 2 SO 2(g) + O 2(g) © 2014 Pearson Education, Inc. 2 SO 3(g) + heat

Exothermic Reaction Equilibrium and Temperature Increasing the temperature of an exothermic reaction • causes the system to respond by shifting the reaction toward removing heat • shifts the reaction toward the reactants, decreasing heat in the system Increase temperature 2 SO 2(g) + O 2(g) © 2014 Pearson Education, Inc. 2 SO 3(g) + heat

Effects of Changing Conditions on Equilibrium © 2014 Pearson Education, Inc.

Learning Check Indicate the shift in equilibrium of each change 2 NO 2(g) + heat 1) toward products 2 NO(g) + O 2(g) 2) toward reactants A. adding NO B. lowering the temperature C. removing O 2 D. increasing the volume E. removing NO © 2014 Pearson Education, Inc.

Solution Indicate the shift in equilibrium of each change 2 NO 2(g) + heat 1) toward products 2 NO(g) + O 2(g) 2) toward reactants A. adding NO (2) toward reactants B. lowering the temperature (2) toward reactants C. removing O 2 (1) toward products D. increasing the volume (1) toward products E. removing NO (1) toward products © 2014 Pearson Education, Inc.