Slide 1 of 21 Chemistry 18.5

© Copyright Pearson Prentice Hall Slide 2 of 21 The Progress of Chemical Reactions During the course of the Tour de France, cyclists travel almost 4000 kilometers with steep mountains at 1600 meters or more. Crossing these high mountains requires extra energy. Chemical reactions can be thought of as processes involving peaks and valleys also. You will learn about the energy of a chemical reaction. 18.5

© Copyright Pearson Prentice Hall The Progress of Chemical Reactions > Slide 3 of 21 Rate Laws What is the general relationship between the value of the specific rate constant, k, and the speed of a chemical reaction? 18.5

Slide 4 of 21 © Copyright Pearson Prentice Hall > The Progress of Chemical Reactions Rate Laws The rate law is an expression for the rate of a reaction in terms of the concentration of reactants. The specific rate constant (k) for a reaction is a proportionality constant relating the concentrations of reactants to the rate of the reaction. 18.5

© Copyright Pearson Prentice Hall The Progress of Chemical Reactions > Slide 5 of 21 Rate Laws The value of the specific rate constant, k, is large if the products form quickly; the value is small if the products form slowly. 18.5

© Copyright Pearson Prentice Hall The Progress of Chemical Reactions > Slide 6 of 21 Rate Laws Animation 24 Observe the characteristics of a first-order reaction.

Slide 7 of 21 © Copyright Pearson Prentice Hall > The Progress of Chemical Reactions Rate Laws In a first-order reaction, the reaction rate is directly proportional to the concentration of only one reactant. As the concentration of that reactant decreases, the rate of the reaction also decreases. 18.5

Slide 8 of 21 © Copyright Pearson Prentice Hall > The Progress of Chemical Reactions Rate Laws 18.5

© Copyright Pearson Prentice Hall Slide 9 of 21 Conceptual Problem 18.2

© Copyright Pearson Prentice Hall Slide 10 of 21 Conceptual Problem 18.2

© Copyright Pearson Prentice Hall Slide 11 of 21 Conceptual Problem 18.2

© Copyright Pearson Prentice Hall Slide 12 of 21 Practice Problems for Conceptual Problem 18.2 Problem Solving Solve Problem 36 with the help of an interactive guided tutorial.

© Copyright Pearson Prentice Hall The Progress of Chemical Reactions > Slide 13 of 21 Reaction Mechanisms What do the hills and valleys in a reaction progress curve represent? 18.5

Slide 14 of 21 © Copyright Pearson Prentice Hall > The Progress of Chemical Reactions Reaction Mechanisms An elementary reaction is a reaction in which reactants are converted to products in a single step. The series of elementary reactions or steps that take place during the course of a complex reaction is called a reaction mechanism. An intermediate is a product of one of the steps in the reaction mechanism. 18.5

Slide 15 of 21 © Copyright Pearson Prentice Hall > The Progress of Chemical Reactions Reaction Mechanisms A reaction progress curve shows an activation- energy peak for each elementary reaction. 18.5

© Copyright Pearson Prentice Hall The Progress of Chemical Reactions > Slide 16 of 21 Reaction Mechanisms The peaks correspond to the energies of the activated complexes. Each valley corresponds to the energy of an intermediate. 18.5

© Copyright Pearson Prentice Hall Slide 17 of 21 Section Quiz -or- Continue to: Launch: Assess students’ understanding of the concepts in Section 18.5 Section Quiz

© Copyright Pearson Prentice Hall Slide 18 of Section Quiz. 1. Choose the correct words for the spaces. If the specific rate constant, k, is _________, then products form __________. a.large, slowly b.large, quickly c.small, quickly d.small, a first order reaction

© Copyright Pearson Prentice Hall Slide 19 of Section Quiz. 2. Choose the correct words for the spaces. In a graph that shows the progress of a reaction, the peaks in the curve correspond to the energies of the _______ and the valleys correspond to the energies of the ________. a.activated complexes, reactants b.intermediates, activated complexes c.reactants, products d.activated complexes, intermediates

© Copyright Pearson Prentice Hall Slide 20 of Section Quiz. 3. Which of the following statements is true? a.Most reactions are elementary reactions. b.In most reactions, reactants are converted to products in a single step. c.Most reactions take place in a series of steps called intermediates. d.Most reactions take place in a series of steps called a reaction mechanism.

© Copyright Pearson Prentice Hall Slide 21 of Section Quiz. 4. The reaction mechanism can best be determined from a.the specific rate constant. b.the overall chemical reaction. c.the rate law. d.experimentation.

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