Slide 1 of 39 Chemistry 18.2

© Copyright Pearson Prentice Hall Slide 2 of 39 Reversible Reactions and Equilibrium In the early 1900s, German chemists refined the process of making ammonia from elemental nitrogen and hydrogen.This process allows the manufacture of nitrogen fertilizers. You will learn how reaction conditions can influence the yield of a chemical reaction. 18.2

© Copyright Pearson Prentice Hall Reversible Reactions and Equilibrium > Slide 3 of 39 Reversible Reactions How do the amounts of reactants and products change in a chemical system at equilibrium? 18.2

© Copyright Pearson Prentice Hall Slide 4 of 39 Reversible Reactions and Equilibrium > Reversible Reactions At chemical equilibrium, no net change occurs in the actual amounts of the components of the system. 18.2

Slide 5 of 39 © Copyright Pearson Prentice Hall Reversible Reactions and Equilibrium > Reversible Reactions If the rate of the shoppers going up the escalator is equal to the rate of the shoppers going down, then the number of shoppers on each floor remains constant, and there is an equilibrium. 18.2

Slide 6 of 39 © Copyright Pearson Prentice Hall Reversible Reactions and Equilibrium > Reversible Reactions A reversible reaction is one in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously. 18.2

© Copyright Pearson Prentice Hall Slide 7 of 39 Reversible Reactions and Equilibrium > Reversible Reactions 18.2 At equilibrium, all three types of molecules are present. SO 2 and O 2 react to give SO 3 SO 3 decomposes to SO 2 and O 2

Slide 8 of 39 © Copyright Pearson Prentice Hall Reversible Reactions and Equilibrium > Reversible Reactions When the rates of the forward and reverse reactions are equal, the reaction has reached a state of balance called chemical equilibrium. The relative concentrations of the reactants and products at equilibrium constitute the equilibrium position of a reaction. 18.2

Slide 9 of 39 © Copyright Pearson Prentice Hall Reversible Reactions and Equilibrium > Reversible Reactions 18.2

© Copyright Pearson Prentice Hall Slide 10 of 39 Reversible Reactions and Equilibrium > Reversible Reactions Animation 23 Take a close look at a generalized reversible reaction.

© Copyright Pearson Prentice Hall Slide 11 of 39 Reversible Reactions and Equilibrium > Factors Affecting Equilibrium: Le Châtelier’s Principle What three stresses can cause a change in the equilibrium position of a chemical system? 18.2

© Copyright Pearson Prentice Hall Slide 12 of 39 Reversible Reactions and Equilibrium > Factors Affecting Equilibrium: Le Châtelier’s Principle Stresses that upset the equilibrium of a chemical system include changes in the concentration of reactants or products, changes in temperature, and changes in pressure. 18.2

Slide 13 of 39 © Copyright Pearson Prentice Hall Reversible Reactions and Equilibrium > Factors Affecting Equilibrium: Le Châtelier’s Principle The French chemist Le Châtelier proposed what has come to be called Le Châtelier’s principle: If a stress is applied to a system in dynamic equilibrium, the system changes in a way that relieves the stress. 18.2

© Copyright Pearson Prentice Hall Slide 14 of 39 Reversible Reactions and Equilibrium > Factors Affecting Equilibrium: Le Châtelier’s Principle Simulation 24 Simulate Le Châtelier’s principle for the synthesis of ammonia.

Slide 15 of 39 © Copyright Pearson Prentice Hall Reversible Reactions and Equilibrium > Factors Affecting Equilibrium: Le Châtelier’s Principle Concentration Rapid breathing during and after vigorous exercise helps reestablish the body’s correct CO 2 :H 2 CO 3 equilibrium, keeping the acid concentration in the blood within a safe range. 18.2

Slide 16 of 39 © Copyright Pearson Prentice Hall Reversible Reactions and Equilibrium > Factors Affecting Equilibrium: Le Châtelier’s Principle Temperature Dinitrogen tetroxide is a colorless gas; nitrogen dioxide is a brown gas. The flask on the left is in a dish of hot water; the flask on the right is in ice. 18.2

© Copyright Pearson Prentice Hall Slide 17 of 39 Reversible Reactions and Equilibrium > Factors Affecting Equilibrium: Le Châtelier’s Principle Pressure Pressure affects a mixture of nitrogen, hydrogen, and ammonia at equilibrium 18.2

© Copyright Pearson Prentice Hall Slide 18 of 39 Conceptual Problem 18.1

© Copyright Pearson Prentice Hall Slide 19 of 39 Conceptual Problem 18.1

© Copyright Pearson Prentice Hall Slide 20 of 39 Conceptual Problem 18.1

© Copyright Pearson Prentice Hall Slide 21 of 39 Practice Problems for Conceptual Problem 18.1 Problem Solving 18.6 Solve a similar problem with the help of an interactive guided tutorial.

© Copyright Pearson Prentice Hall Reversible Reactions and Equilibrium > Slide 22 of 39 Equilibrium Constants What does the value of K eq indicate about the equilibrium position of a reaction? 18.2

Slide 23 of 39 © Copyright Pearson Prentice Hall Reversible Reactions and Equilibrium > Equilibrium Constants The equilibrium constant (K eq ) is the ratio of product concentrations to reactant concentrations at equilibrium, with each concentration raised to a power equal to the number of moles of that substance in the balanced chemical equation. 18.2

© Copyright Pearson Prentice Hall Slide 24 of 39 Reversible Reactions and Equilibrium > Equilibrium Constants A value of K eq greater than 1 means that products are favored over reactants; a value of K eq less than 1 means that reactants are favored over products. 18.2

© Copyright Pearson Prentice Hall SAMPLE PROBLEM Slide 25 of

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© Copyright Pearson Prentice Hall Slide 29 of 39 Practice Problems for Sample Problem 18.1 Problem Solving 18.7 Solve Problem 7 with the help of an interactive guided tutorial.

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© Copyright Pearson Prentice Hall Slide 34 of 39 Practice Problems for Sample Problem 18.2 Problem Solving 18.9 Solve Problem 9 with the help of an interactive guided tutorial.

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