Chemistry 18.5

The rate of rxns depends in part on the concentration of the reactants.

The rate law is an expression for the rate of a reaction in terms of the concentration of reactants.

18.5 Rate Laws 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 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.

Zeroith Order: No Change 18.5 Rate Laws Zeroith Order: No Change First Order: Initial rate of the rxn doubles as reactant is doubled Second Order: Initial rate of rxn quadruples when reactant is doubled Third Order: Initial rate of rxn increases eightfold when rxn is doubled

https://www.youtube.com/watch?v=iaFgU 3DP2S8

18.5 Rate Laws The graph shows how the concentration of a reactant changes as a reaction proceeds. INTERPRETING GRAPHS a. Navigate What is the dependent variable? b. Read What happens to the relative concentration of reactant A as time progresses? c. Interpret The short colored lines illustrate the reaction rates at two distinct points of time. Is the initial rate or the subsequent rate faster?

Conceptual Problem 18.2

for Conceptual Problem 18.2 Problem Solving 18.36 Solve Problem 36 with the help of an interactive guided tutorial.

18.5 Reaction Mechanisms Reaction Mechanisms What do the hills and valleys in a reaction progress curve represent?

18.5 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 Reaction Mechanisms A reaction progress curve shows an activation- energy peak for each elementary reaction. A reaction progress curve shows an activation-energy peak for each elementary reaction. Valleys indicate the formation of intermediates. INTERPRETING GRAPHS a. Navigate How many elementary reactions are part of this reaction? b. Read How many intermediates are formed? c. Interpret How would a catalyst affect the energy of the reactants and the energy of the products of this reaction?

18.5 Reaction Mechanisms The peaks correspond to the energies of the activated complexes. Each valley corresponds to the energy of an intermediate.

18.5 Section Quiz. 18.5.

18.5 Section Quiz. 1. Choose the correct words for the spaces. If the specific rate constant, k, is _________, then products form __________. large, slowly large, quickly small, quickly small, a first order reaction

18.5 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 ________. activated complexes, reactants intermediates, activated complexes reactants, products activated complexes, intermediates

18.5 Section Quiz. 3. Which of the following statements is true? Most reactions are elementary reactions. In most reactions, reactants are converted to products in a single step. Most reactions take place in a series of steps called intermediates. Most reactions take place in a series of steps called a reaction mechanism.

18.5 Section Quiz. 4. The reaction mechanism can best be determined from the specific rate constant. the overall chemical reaction. the rate law. experimentation.

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