EXAM 3 STUDY GUIDE

The exam will consist of 20 multiple choice questions with 70% “C” questions, 20% “B” questions, and 10% “A” questions. In general, “C” questions are those involving the most basic concepts, particularly ones that you have used before. “C” calculation problems typically involve one major step with 1-2 more minor steps. (Examples of minor steps would be calculating molecular weights or converting [H₃O⁺] to pH.) “B” questions involve more difficult concepts, particularly ones that are new. “B” calculation questions typically involve at least two major steps with 1-4 minor steps. “A” questions are those involving the most difficult concepts or those that require a thorough understanding in order to answer correctly. Often “A” questions require bringing together different concepts to solve the problem and 2+ calculation steps. Note also that concepts listed under the “C” or “B” categories below can be converted to harder questions, depending on how I ask the question.

Background Concepts [Homework Examples]

• Know the molecular formulas and charges of common ions. [Common Ion handout]
• Calculate molar mass, convert between grams and moles using the molar mass. [Problem Set 1]
• Calculate concentrations in molarity, convert between liters and moles using molarity. [Problem Set 1, Quiz 2]
• Calculate concentrations after dilution. [Exp. 2]

“C” Questions [Homework Examples]

Chapter 17:

• Know what “oxidation” and “reduction” mean.
• Determine oxidation numbers; decide what is being oxidized and what is being reduced; identify oxidizing and reducing agents. [17.3, 17.7, 17.9, quiz 7’s]
• Balance oxidation-reduction reactions in acidic or basic solution. [17.6, 17.8, quiz 7’s]
• Understand the basics of how an electrochemical cell works. [exp. 6, S19 ex3a.9]
• Know what “electrode”, “anode” and “cathode” mean.
• Understand the shorthand notation for electrochemical cells. [17.13, 17.15]
• Be able to determine the overall reaction occurring in a given electrochemical cell and vice versa:

construct an electrochemical cell in which a given oxidation reduction reaction will occur. [17.13,

17.15, quiz 8’s]

• Calculate E°_cell from E° values. [17.23, 17.25, 17.27, PS5, quiz 8’s]
• Calculate ΔG° and K from E°_cell and vice versa. [F20 quiz 7]
• Use E° values to predict which in a series of compounds will be the best oxidizing or reducing agent.[quiz 8’s] Chapter 12:
• Know the relationship between reaction rates for different reaction components. [12.3, 12.6, S20 quiz 8]
• Know what the rate law, reaction order and rate constant are. [quiz 9’s]
• Calculate k from rate law, knowing initial rate and concentrations. [quiz 9’s]
• Calculate rate at particular reactant concentrations, knowing rate law and value of rate constant.
• Determine rate law from initial rate data. [12.23, 12.25, quiz 9’s]
• Use the integrated rate law for a first order reaction. [PS6, quiz 9’s,]
• Use the integrated rate law for a second order reaction. [PS6, quiz 9’s]
• Know how to distinguish between zero, first and second order reaction from concentration vs. time data using integrated rate laws. [12.33, 12.35, PS6, quiz 9’s]
• Know how temperature affects rates.
• Be familiar with the Arrhenius equation. Know what the frequency factor and activation energy represent and how they relate to the rate constant. What is the physical significance of the e ^Ea/(RT) fraction in the Arrhenius equation.
• What is an elementary reaction according to collision theory?
• According to collision theory, what 3 criteria need to be met in order for an elementary reaction to occur?
• What is a unimolecular elementary reaction? What is a bimolecular elementary reaction? What is a termolecular elementary reaction? Why is a termolecular elementary reaction so unlikely according to collision theory?
• Know the basic concept behind transition state theory and what the transition state represents.
• Be able to construct and/or interpret a simple reaction coordinate diagram for an elementary reaction; know where the transition state is and how to determine E_a,f and E_a,r, ΔG_rxn from the diagram. [S20ex3.18]
• What is an elementary reaction according to transition theory?
• Be able to construct and/or interpret a reaction coordinate diagram for a multi-step reaction and understand how it relates to the mechanism. [F19ex3a.12; S20ex3.19]
• Know what the significance of the slow or “rate-determining step” in a reaction is.

“B” Questions [Homework Examples]

Concepts listed under the “C” category can be converted to B questions by combining them and/or requiring a better understanding of the concept in order to be solved.

Chapter 17:

• Calculate E_cell under non-standard conditions using Nernst equation. [PS5, WS3, old quiz8’s]
• Less straightforward problems using the Nernst equation, e.g. calculating concentrations from E_cell values. [PS5] Chapter 12:
• Understand important concepts behind collision theory: What does the concentration term in the rate law of an elementary reaction represent? why does increasing the molecular size of a reactant generally lead to a decrease in reaction rates? What does the activation energy represent according to collision theory? Why do the rates of elementary reactions increase with temperature?

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“A” Questions (Homework Examples)

Concepts listed under the “C” or “B” categories can be converted to A questions by combining them and/or asking the question in such a way that the route to the answer is not straightforward and requires a thorough understanding of the concepts.

Chapter 17:

• Calculate K’s and ΔG°’s using E° values, and vice versa, harder examples. [F19ex3a.20] Chapter 12:
• Understand the concepts behind “pseudo-order” reactions and how the integrated rate laws can be used to determine more complicated rate laws using pseudo-order conditions. [PS6, Exp. 7]

Information that will be given with exam:

Table of E° values.

Chapter 17 and 12 equations.