Chem 128 Assignments

ASSIGNMENT 1 [complete by 1/22/04]

GUIDED READING:

1. Read Section 10.1 (pp. 257-261) on concentration units. Define molarity, mole fraction, mass percent (ppm, ppb), and molality. Study Examples 10.1 through 10.3 carefully. Refer also to the in-class exercise. Study carefully Exercise 10.4 about conversions between concentration units. Now try the following problems (answers in the back) on pp. 276-78: 2, 6, 8, 14, 18.

2. Read Section 10.2 (pp. 261-264) on factors that affect solubility. What is the meaning of the statement "like dissolves like"? How is this related to the intermolecular forces you studied at the end of Chem 127 (see Section 9.3 to review them)? Examine the trend shown in Table 10.1 and explain it in terms of molecular structures and intermolecular forces. For most ionic substances, what happens to their solubility in water as temperature is increased? For gases, what happens to their solubility in water as temperature is increased? How are these trends related to the following statement: An increase in temperature always shifts the position of an equilibrium to favor an endothermic process. [Review Section 8.1 for a definition of endothermic processes.] In what kind of system does pressure have a major effect on solubility? What is Henry's Law? Study carefully Example 10.5. Now try the following problems (answers in the back) on pp. 277-78: 20, 26.

HOMEWORK PROBLEMS: 9, 13, 17, 19, 25

ASSIGNMENT 3 [complete by 2/03/04]

GUIDED READING:

1. Read Section 11.1 (pp. 283-285) on the meaning of a reaction rate. Define reaction rate. Study Figures 11.1 and 11.2 carefully. How do you determine an instantaneous rate at a particular concentration of reactant? Try Problems 2, 4 and 18 on pp. 311-312, and check your answers in the back of the book.

2. Read Section 11.2 (pp. 286-290) on reactant rate and concentration. Why does reaction rate depend on reactant concentration? What is a rate expression? a rate constant? What indicates the order of reaction with respect to a particular reactant? How do you determine the overall order of a reaction from its rate expression? Why can you not determine the overall order of a reaction from the coefficients of the balanced equation for the reaction? How do you determine the order of a reaction for each reactant? Study Example 11.1 (p. 288) and Example 11.2 (p. 289) carefully. Now try Problems 22 and 24, and check your answers in the back of the book.

HOMEWORK PROBLEMS: 1, 3, 17, 21, 23

ASSIGNMENT 4 [complete by 2/5/04]

GUIDED READING:

1. Read Section 11.3 (pp. 290-293) on the relationship of reactant concentration to time elapsed. What is the relationship between reactant concentration and time in a first-order reaction? What function of reactant concentration do you plot on the y-axis vs time on the x-axis to get a straight line? Is the slope of the line positive or negative? Define half-life of a reaction. What formula describes the half-life of a first order reaction? For a first-order reaction, does the half-life depend on the concentration of reactant? Study Example 11.3 (pp. 291-92) carefully. What are the units for the rate constant, k, of a first-order reaction? Radioactive decay is a first-order process. Study Example 11.4 (pp. 292-93) carefully. Note that mole fractions can be used in place of molarities as expressions of concentration. Try any or all of Problems 32-42 even and check your answers in the back of the text.

2. Read Section 11.3 (pp. 293-295) on zero- and second-order reactions. What function of reactant concentration do you plot against time to get a straight line for a zero-order reaction? a second-order reaction? What is the half-life expression for a zero-order reaction? a second-order reaction? Study Examples 11.5 and 11.6 carefully. Now try Problems 44, 46, and 48 and check your answers in the back of the text.

3. Read Section 11.4 (pp. 295-298) on models for reaction rate. Describe the "collision model" of reaction rates. What is activation energy? According to the collision model, what two factors are important in determining whether a collision will result in reactant molecules going on to form product molecules? What are p, Z, and f in the definition of a rate constant k = p x Z x f? Where does the activation energy E_a fit into this expression, and how is the activation energy related to reaction rate? Describe the "transition-state model" of reaction rates. What is found in an energy diagram for a reaction? What is an activated complex and where is it shown on a reaction energy diagram? Look at Table 11.3 to compare the two models for reaction rates. Which model appears to be more accurate in predicting the observed rate constant k for chemical reactions?

HOMEWORK PROBLEMS: 31, 33, 35, 39, 43, 45

ASSIGNMENT 5 [complete by 2/10/04]

GUIDED READING:

1. Read Section 11.5 (pp. 299-302) on the relationship of reaction rate to temperature. In general, what happens to the rate of a reaction when the temperature at which it is run is increased? decreased? Study Figure 11.9 (p. 300). How is collision energy related to temperature? What variables are related in the Arrhenius equation? Study Figure 11.10 (p. 300). What information can be obtained from an Arrhenius plot? What information is in the slope of the straight line? Study the two-point equation relating the rate constant to T (p. 301) and study Example 11.7 (pp. 301-302). Now try Problems 50 and 56 and check your answers in the back of the text.

2. Read Section 11.6 (pp. 302-304) on catalysis. What is a catalyst? How does it increase the rate of a reaction? What is a heterogeneous catalyst? What is a homogeneous catalyst? What is an enzyme ?

3. Read Section 11.7 (pp. 304-307) on reaction mechanisms. What is a reaction mechanism? What is an elementary step in a reaction mechanism? Can you write the rate expression for an elementary step directly from the balanced reaction equation for that step? Why? What is a unimolecular step? a bimolecular step? a termolecular step? What is a rate-determining step? How do you deduce a rate expression from a proposed reaction mechanism? Study the example on p. 306. What is an intermediate? An intermediate cannot appear in a rate for a reaction. How do you eliminate intermediates from the rate expression? Study Example 11.8 (p. 307). Can a reaction mechanism be proven experimentally? Now try Problems 60 and 62 and check your answers in the back of the text.

HOMEWORK PROBLEMS: 49, 55, 59, 61, 63

ASSIGNMENT 6 [complete by 2/19/04]

GUIDED READING:

1. Read Section 12.1 (pp. 321-324) on the N₂O₄-NO₂ gaseous equilibrium system. What is dynamic equilibrium? What is true of the forward and backward rates for a reversible reaction at equilibrium? What is the equilibrium constant K?

2. Read Section 12.2 (pp. 324-328) on the equilibrium constant expression. How is the equilibrium constant expression written for a reaction in which both reactants and products are gases? How is the equilibrium constant K dependent on the way in which the reaction equation is written? What is the coefficient rule? the reciprocal rule? What is the rule of multiple equilibria? Does it remind you of another "Law" you learned last term? (Hint: it is on the chapter on thermochemistry.) Read the section on heterogeneous equilibria. Do pure solids or pure liquids affect the position of equilibrium in a reversible reaction? Do terms for these species show up in the equilibrium constant expression? What about solutes and ions in aqueous solution? How do they appear in the equilibrium constant expression? Now try the following problems at the end of the chapter and check your answers in the back: 2, 6, 8, 12, 14, 16, 18

HOMEWORK PROBLEMS: 1, 5, 7, 11, 13, 15

ASSIGNMENT 7 [complete by 2/24/04]

GUIDED READING:

1. Read Section 12.3 (pp. 329-330) on determination of the equilibrium constant K. Study Example 12.3. What is the first step in determining the equilibrium constant, given the balanced reaction equation and equilibrium pressures of reactants and products? What is the next step? Study Example 12.4. Given original pressures of reactants and products and the equilibrium pressure of one species, how do you generate the information you need to determine K? What provides a guideline for generating this information? Now try Problems 20, 22 and 24 and check your answers in the back of the text.

2. Read Section 12.4 (pp. 330-334) on applications of the equilibrium constant. What is a reaction quotient? How does the value of the quotient Q compare to that of K when a reaction is at equilibrium? If Q < K, what does that tell you about the reaction? If Q > K, in which direction will the equilibrium of the reaction shift? Study Example 12.5 on calculation of a reaction quotient and interpreting the result. Now try Problems 26 and 28 and check your answers in the back of the text. Study Example 12.6 carefully. How is information generated, using K and initial pressures of reactants and products, to determine the equilibrium concentrations of reactants and products? Look carefully at the tables and be sure you understand how the algebraic expressions were generated. Now try any of the even numbered problems from 30 through 42 and check your answers in the back of the text. Do enough of these problems to be sure you understand the process.

HOMEWORK PROBLEMS: 19, 23, 25, 29, 31, 35, 41

ASSIGNMENT 8 [complete by 3/2/04]

GUIDED READING:

1. Read Section 12.5 (pp. 334-339) on the effect of changes in conditions on an equilibrium system. What is Le Chatelier's Principle? What is the effect of adding or removing a reactant or product gas from a system that is at equilibrium? Study Example 12.7. Is Q = K after such an addition or removal? How do you get the information needed to calculate the new equilibrium pressures? What happens to a system at equilibrium if you change the pressure on the system by changing the volume? Study Tables 12.5 and 12.6. If you add an inert gas such as Helium to the system, does that affect the equilibrium of the system? Why or why not? How does changing the temperature of the system affect the equilibrium? If the temperature is increased, what happens to the equilibrium in an endothermic system? in an exothermic system? Study the van't Hoff equation and Example 12.8. Now try Problems 44 through 52 even and check your answers in the back of the text. Do enough of them to be sure you understand them.

2. Read Section 13.1 (pp. 351-352) on the Brønsted-Lowry acid-base model. According to this model, what is an acid? a base? What happens in an acid-base reaction? What is a conjugate acid-base pair? How does an acid differ from its conjugate base? What is an an amphiprotic species? Study Example 13.1. Now try parts of Problems 2, 4, and 6 and check your answers in the back of the text.

3. Read Section 13.2 (pp. 352-353) on the ion product of water. What is the equilibrium constant expression for the self-ionization of water? What is the ion product constant of water? What is K_w at 25°C? What are [H⁺] and [^-OH] in a neutral solution? What is the relationship between [H⁺] and [^-OH] in an acidic solution? in a basic solution?

4. Read Section 13.3 (pp. 353-357) on pH and pOH. What is the relationship of pH to [H⁺]? of pOH to [^-OH]? What is the relationship between pH and acidity? What is the pH of a neutral solution? Study Figure 13.2 carefully. What is the sum of pH and pOH at 25°C in an aqueous solution? What is the product of [H⁺] and [^-OH] at 25°C in an aqueous solution? Study Example 13.2. Now try parts of Problems 8-16 even and check your answers in the back of the text. What is a strong acid? a strong base? Study Example 13.3 carefully. Now try at least one of the following: Problems 18, 20, 22, and 24, and check your answers in the back of the text.

5. Read Section 13.4 (pp. 357-361) on weak acids and their equilibrium constants. What is a weak acid? What kinds of species are weak acids? Write the equilibrium constant expression for a generalized weak acid. What does the a stand for in the equilibrium constant K_a? What is a pK_a? What is the relationship between K_a and acid strength? between pK_a and acid strength? Study table 13.2 for trends. Study Example 13.4. Now try parts of Problems 26-32 even and check your answers in the back of the text. Study Example 13.5, and the definition of percent ionization. Now try Problems 34 and 36 and check your answers in the back of the text.

HOMEWORK PROBLEMS:

Chapter 12: 43, 47, 49

Chapter 13: 1-11 odd, 15, 17, 19, 25acd, 27, 33, 35

ASSIGNMENT 9 [complete by 3/16/04]

GUIDED READING:

1. Read Section 13.4, pp. 361-365 on calculation of [H⁺] in weak acid solutions. Study Example 13.7. Why is it usually all right to ignore x in the denominator of the K_a expression when determining [H⁺] in weak acid solutions? When is it not safe to ignore x? What two methods can be used to solve for [H⁺] when the percent ionization is greater than 5%? Study Example 13.8. How do you find [H⁺] of a weak polyprotic acid? Study Example 13.9 and Table 13.3. Now try Problems 40, 42, and 48 and check your answers in the back of the book.

2. Read Section 13.5, pp. 365-368, on weak bases and their equilibrium constants. What kinds of substances behave as weak bases? Study Example 13.10. Try parts of Problem 50 and check your answers in the back. What is a K_b? a pK_b? How do you calculate the [H⁺] of an aqueous solution of a weak base? What does x represent in the calculation? Study Example 13.11. What is the relationship between K_b of a weak base and K_a of the conjugate acid of the weak base? Study Table 13.4. Try Problems 51, 54, and 56, and check your answers in the back of the book.

3. Read Section 13.6, pp. 368-370, on acid-base properties of salt solutions. What is the definition of a salt? What is an acidic cation? a basic anion? a spectator ion? When is the aqueous solution of a salt acidic?, basic? neutral? If a salt contains an acidic cation and a basic anion, how do you determine which one will dominate the pH of the solution? Study Table 13.5 and Example 13.12.Now try Problem 60 and check your answers in the back of the book.

4. Read Section 14.1, pp. 379-383, on buffers. What two chemical species are found in a buffer? What are two important properties of a buffer? What equilibrium expression is used in determining the [H⁺] of a buffer? In a buffer, the concentrations of [HB] and [B^-] are usually very similar. Why can these concentrations be expressed as moles of HB and moles of B^-? Study Example 14.1. What are the important things to consider in choosing an acid-base pair for a buffer? Study Example 14.2. Now try Problems 2 and 10, and check your answers in the back of the book.

HOMEWORK PROBLEMS:

CHAPTER 13: 39, 41, 47, 49, 51, 53, 55, 59

CHAPTER 14: 9

ASSIGNMENT 10 [complete by 3/18/04]

GUIDED READING:

1. Read Section 14.1, pp. 383-385 on buffers. How does added strong acid or strong base affect the pH of a buffer? How do you calculate this effect? Study Example 14.3. What affects the capacity of a buffer to absorb strong acid or base? Try Problem 26 and check your answer in the back of the book.

2. Read Section 14.2, pp. 386-388, on acid-base indicators. What is an acid-base indicator? What is it used for? What is the equivalence point in a titration? What is an endpoint? Under what conditions will you see the acid color of the indicator? the basic color? a color inbetween? What two factors does the ratio of HIn to In^- depend? Study Example 6.5. Try Problem 40 and check your answer in the back of the book.

3. Read Section 14.3, pp. 388-393, on acid-base titrations. For the titration of a strong acid with a strong base, what determines the pH of the solution being titrated before the titration begins? What is the pH of the solution formed at the equivalence point? (Why?) What is the net ionic equation for all titrations of this sort? How do you calculate the pH of the solution at the midpoint of the titration? Study Example 14.6. Now try Problem 44 and check your answers in the back of the book. When a weak acid is titrated with a strong base, how is the pH of the solution determined before any base is added? What is the pH at the midpoint of the titration? (Why?) Is the pH at the equivalence point 7, higher than 7, or lower than 7? Why? Examine Example 14.7. When a weak base is titrated by a strong acid, how do you determine the pH of the solution before any acid is added? What is the pH at the midpoint of the titration? Why? Is the pH of the solution at the equivalence point 7, higher than 7, or lower than 7? Why? Try Problem 46 and check your answer in the back of the book. Study the summary Table 14.3 carefully.

HOMEWORK PROBLEMS:

CHAPTER 14: 11, 13, 15, 19, 25, 39, 43, 45

ASSIGNMENT 11 [complete by 4/1/04]

GUIDED READING:

1. This chapter deals with the equilibria that govern the solubility of slightly soluble ionic compounds in water. Read Section 16.1, pp. 425-428 on precipitate formation, the equilibrium concentration of ions, and the solubility constant. What is a solubility product constant? a solubility product? Study Example 16.1. Try Problems 2 and 4, and check your answers in the back of the book. Study Example 16.2 on using K_sp to find the equilibrium concentrations of ions in solution. Try Problem 6 and check your answers in the back of the book. Given a K_sp and the concentrations of the compound ions in solution, one can find Q and compare it to K_sp to determine whether some of the compound will precipitate out or whether all of it will stay dissolved in water. What happens if Q is greater than K_sp? Smaller? Equal to? Study Example 16.3. Then try Problems 10 and 14, and check your answers in the back of the book.

2. Read Section 16.1, pp. 428-430, on water solubility and the common ion effect. The K_sp of a compound is not the same as its solubility. How can the K_sp expression be used to figure out the solubility of a compound in moles per liter? Study Example 16.4 carefully. Now try Problems 16 and 18a, and check your answers in the back of the book. What is the common ion effect? Study Example 16.5 carefully. Now try Problem 18bc, and check your answer in the back of the book.

HOMEWORK PROBLEMS:

CHAPTER 16: 1, 3, 5, 9, 11, 15, 17, 19

ASSIGNMENT 12 [complete by 4/8/04]

GUIDED READING:

1. Read Section 17.1 (pp. 445-447) on spontaneous processes. What is a spontaneous process? What two factors contribute to making a process spontaneous? Try Problem 2, and check your answers in the back of the book.

2. Read Section 17.2 (pp. 447-451) on entropy. What is entropy? What is the symbol for this thermodynamic quantity? What are its units? What factors contribute to a state of higher entropy? When does a substance have an entropy of zero? Study Example 17.1, and try Problems 6 and 8. Check your answers in the back of the book. What are standard molar entropies? How can they be used to calculate the standard entropy change for a reaction? Study Example 17.2, and try Problems 12 and 14. Check your answers in the back of the book. What does the Second Law of Thermodynamics say about the relationship between entropy change in a system and its surroundings, and spontaneity?

3. Read Section 17.3 (pp. 452-454) about Free Energy, G. What is Gibbs free energy? Is it a state property? Is it an extensive property? How is it related to enthalpy, entropy, and temperature? How is DG used to determine whether or not a reaction is spontaneous? What is the Gibbs-Helmholtz equation? What signs of the enthalpy change and the entropy change are associated with spontaneous reactions?

4. Read Section 17.4 (pp. 454-457) on the standard free energy change, DG°. What is the standard free energy change? What are standard conditions for this quantity? What is the sign of DG° for a spontaneous reaction under standard conditions? What does it mean if DG° = 0? Study Example 17.3 and use any one of the reaction equations in Problem 12 to calculate DG° using the same method as in the example. What is DG°_f for a compound? When can the tabulated values of DG°_f be used to calculate the standard free energy change for a reaction? Study Example 17.4 and try Problem 22. Check your answers in the back of the book. How is DG° calculated at some temperature other than 25°C? Study Example 17.5 and try Problem 18. Check your answers in the back of the book. For flexibility and understanding of concepts, try any of the following: Problems 26, 28, and 30. Check your answers in the back of the book.

HOMEWORK PROBLEMS:

CHAPTER 17: 1, 5, 7, 11, 15, 17, 21, 25, 27, 31

ASSIGNMENT 13 [complete by 4/15/04]

GUIDED READING:

1. Read Section 17.5 (pp. 457-461) on the effect of temperature, pressure and concentration on reaction spontaneity. Examine the Gibbs-Helmholtz equation. In which two cases does temperature not affect the spontaneity of a reaction? In which two cases does temperature affect the spontaneity of a reaction? For the cases in which temperature does affect spontaneity, how do you determine the temperature at which the DG changes sign? Study Example 17.6. Then try Problems 34 and 38 and check the answers in the back of the book. When DG is calculated at a nonstandard pressure or concentration of reactants and products, how is the effect on DG calculated? Study Example 17.7 carefully. Now try Problem 52 and check your answer in the back of the book.

2. Read Section 17.6 (pp. 461-462) on the relationship between DG and K. What equation can be used to characterize this relationship? If DG is negative, what is true of K? If DG is positive, what is true of K? Study Example 17.8 carefully. Now try Problems 62 and 64, and check your answers in the back of the book.

3. Read Section 17.7 (pp. 462-464) about free energy changes and coupled reactions. A nonspontaneous reaction can be made to go by coupling it with a spontaneous reaction. Why is this so? Examine the examples in this section and Example 17.9. Now try Problems 56 and 58, and check your answers in the back of the book.

HOMEWORK PROBLEMS:

CHAPTER 17: 33, 35, 39, 43, 49, 51, 55, 61, 63

ASSIGNMENT 14 [complete by 4/20/04]

GUIDED READING:

1. Read Section 18.1 (pp. 475-479) on voltaic cells. What is a voltaic cell? a half-cell? Define the terms electrode, anode, cathode, oxidation, reduction, salt bridge. Study Example 18.1 and Figures 18.3 and 18.4 carefully. Try parts of Problems 2 and 4, and check your answers in the back of the book.

2. Read Section 18.2 (pp. 479-484) on standard voltages. What are standard conditions for a voltaic cell? What are standard voltages? standard potentials? What is an oxidizing agent? a reducing agent? Where can you locate the best oxidizing agents in a table of standard potentials? Where can you locate the best reducing agents in such a table? Study Example 18.2. Try Problems 8 and 10 and check your answers in the back of the book. How do you calculate the standard potential, E°, of a voltaic cell from standard reduction and oxidation potentials? Study Example 18.3. Do you have to multiply the oxidation or reduction potentials by the coefficients in the balanced equation before adding them together? How do you use E° for an electrochemical cell to decide whether the cell is a voltaic cell (i.e. whether the reaction is spontaneous)? Study Example 18.4. Try Problems 16 and 24 and check your answers in the back of the book.

3. Read Section 18.3 (pp. 484-486) on relationships between E°, DG°, and K. What equation expresses the relationship between E° and DG°? What is n in this equation? What is F? What is the value of R in this equation? What are its units? What are the signs of E° and DG° for a spontaneous reaction? What equation expresses the relationship between DG° and K? What equation expresses the relationship between E° and K? Study Examples 18.4 and 18.5. Try Problems 34 and 38, and check your answers in the back of the book.

4. Read Section 18.4 (pp. 486-489) on the effect of concentration on voltage. What is the Nernst equation, and under what circumstances is it used? If Q in the Nernst equation is greater than 1, what does that mean? What is the case when Q is less than 1? equal to 1? Study Examples 18.6 and 18.7 (on using the Nernst equation to determine ion concentrations). Try Problems 44 and 52, and check your answers in the back of the book.

5. Read Section 18.5 (pp. 489-493) on electrolytic cells. What is an electrolytic cell? What is electrolysis? What units express the following: quantity of electrical charge, rate of current flow, amount of electrical energy? What is a kWh? Study Example 18.8. Try Problems 58 and 60, and check your answers in the back of the book.

6. Read Section 18.6 (pp. 493-497) on commercial cells. What is the most important commercial electrolysis reaction? What does it produce? What is a primary voltaic cell? a storage cell? a fuel cell? How are these electrochemical cells alike? How are they different?

HOMEWORK PROBLEMS:

CHAPTER 18: 1, 3a, 7, 9, 15, 23, 33, 37, 43, 55, 57, 59a

ASSIGNMENT 15 [this one will not be collected]

GUIDED READING:

1. Read Section 19.1 (pp. 507-512) on radioactivity. What is radioactivity? What is an alpha particle? a beta particle? gamma radiation? a positron? How do emissions of these particles or radiation affect the radioactive nucleus? What is K-electron capture? Study Example 19.1. Try Problem 4 and check your answers in the back of the book. What is a bombardment reaction? What are transuranium elements? Try Problem 10 and check your answers in the back of the book. What are some ways in which radioactive nuclei are used?

2. Read Section 19.2 (pp. 512-514) on rate of radioactive decay. Radioactive decay is first order process. Review in Chapter 2 the rate laws for first order processes. What other measures of amount are substituted for molarities in the rate equations for radioactive decay? What is activity and what are its units? What is a Bq? a Ci? What is the basis for C-14 dating? Study Examples 19.2 and 19.3. Try a few of the problems 14-22 even, and check your answers in the back of the book.

3. Read Section 19.3 (pp. 514-518) on mass-energy relations. What equation defines the relationship between energy and mass in a nuclear reaction? Why is so much energy released in a nuclear reaction compared to the energy released in an ordinary chemical reaction? Study Example 19.4. What is nuclear binding energy? Study Example 19.5 and Figure 19.4. Where on Figure 19.4 are the nuclei that are the most stable? Which nuclei, according to this figure are most likely to undergo fission? fusion? Try Problems 32-36 even and check your answers in the back of the book.

4. Read Section 19.4 (pp. 518-521) on nuclear fission. What is nuclear fission? What is involved in the fission process for U-235? What is a critical mass? What subatomic particles are responsible for maintaining a chain reaction? How is a sustained nuclear fission reaction (for energy, in a nuclear reactor) different from the nuclear reaction that occurs when a bomb is detonated?

5. Read Section 19.5 (pp. 521-523) on nuclear fusion. What is nuclear fusion? Where does this process occur in nature? What are some of the difficulties in leashing nuclear fusion to provide energy (as in a power plant)?

HOMEWORK PROBLEMS:

CHAPTER 19: 3, 11, 17, 19, 21, 25, 31, 33, 35, 37

ASSIGNMENTS