5 Steps to a 5 AP Chemistry

Step 1: ClO 2 +ClO 2 →Cl 2 O 4

Step 2: Cl 2 O 4 +OH−→ClO 3 −+HClO 2

Step 3: HClO 2 +OH−→ClO 2 −+H 2 O

Total: 2 ClO 2 +Cl 2 O 4 +2 OH−+HClO 2

→Cl 2 O 4 +ClO 3 −+HClO 2 +ClO 2 −+H 2 O

After removing the intermediates (Cl 2 O 4 and HClO 2 ):

2 ClO 2 +2 OH−→ClO 3 −, +ClO 2 −+H 2 O

As this matches the original reaction equation, the mechanism fulfills the overall stoi-

chiometry requirement. Give yourself 1 point if you have done this.

The total is 10 points for this question. Subtract one point if any answer has an incor-

rect number of significant figures.

 Rapid Review

 Kinetics is a study of the speed of a chemical reaction.

 The five factors that can affect the rates of chemical reaction are the nature of the reac-

tants, the temperature, the concentration of the reactants, the physical state of the reac-

tants, and the presence of a catalyst.

 The rate equation relates the speed of reaction to the concentration of reactants and has

the form: Rate =k[A]m[B]n... where kis the rate constant and mand nare the orders

of reaction with respect to that specific reactant.

 The rate law must be determined from experimental data. Review how to determine the

rate law from kinetics data.

 When mathematically comparing two experiments in the determination of the rate equa-

tion, be sure to choose two in which all reactant concentrations except one remain constant.

 Rate laws can be written in the integrated form.

 If a reaction is first order, it has the rate law of Rate =k[A]; ln [A]t–ln [A] 0 = –kt; a plot

of ln[A] versus time gives a straight line.

 If a reaction is second order, it has the form of (integrated

rate law); a plot of versus time gives a straight line.

 The reaction half-life is the amount of time that it takes the reactant concentration to

decrease to one-half its initial concentration.

 The half-life can be related to concentration and time by these two equations (first and

second order, respectively): and t1/2= 1/k[A] 0 to apply these equations.

 The activation energy is the minimum amount of energy needed to initiate or start a

chemical reaction.

 Many reactions proceed from reactants to products by a series of steps called elementary

steps. All these steps together describe the reaction mechanism, the pathway by which

the reaction occurs.

 The slowest step in a reaction mechanism is the rate-determining step. It determines the

rate law.

 A catalyst is a substance that speeds up a reaction without being consumed in the reaction.

 A homogeneous catalyst is in the same phase as the reactants, whereas a heterogeneous

catalyst is in a different phase from the reactants.

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210  Step 4. Review the Knowledge You Need to Score High