Study Guide for Module 16—Thermodynamics · Study Guide for Module 16—Thermodynamics ... Reading Assignment: Chapter 16 in Chemistry, 6th Edition by Zumdahl. Guide for Your Lecturer:

Chemistry 1020, Module 16 Name

Study Guide for Module 16—Thermodynamics

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Reading Assignment: Chapter 16 in Chemistry, 6th Edition by Zumdahl.

Guide for Your Lecturer:

1. Review (Internal Energy, Enthalpy, Kinds of work, Laws of thermochemistry)2. Spontaneity, Factors Which Tend to Cause Reactions to Be Spontaneous, and Entropy3. The Laws of Thermodynamics4. An Overview of the Relationship Between Spontaneity and Gibbs Free Energy

✔ 5. Predicting the Signs on Changes in Entropy, Enthalpy, and Free Energy for Familiar Reactions✔ 6. More Practice Predicting the Signs on Changes in Entropy, Enthalpy, and Free Energy✔ 7. Calculating Change in Free Energy from Changes in Entropy and Enthalpy✔ 8. Temperature Dependence of Spontaneity✔ 9. Relationship Between Standard Free Energy and Cell Potentials✔ 10. Relationship Between Standard Free Energy and Equilibrium Constant

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HomeworkNote: ✔ indicates problems to be stressed on drill quizzes and hour exams.■Review From Module 61a) Define internal energy. (E = The sum of the kinetic and potential energies of the system under study.)

-----------------------------------------------------------------------------------------------------------------------------------------------b) List the four ways in which the internal energy of a system can be changed. (1. Heat (q) can flow in. 2.

Heat can flow out. 3. Work (w) can be done on the system. 4. Work can be done by the system.)• •

• •

-----------------------------------------------------------------------------------------------------------------------------------------------c) What are the two kinds of work which can be done by or on a chemical system. (PV work as in expansion of a

gas and electrical work as when a battery is used to run a motor.)• •

-----------------------------------------------------------------------------------------------------------------------------------------------d) How is the change in the internal energy of a system related to heat change (q) and work done by or on the

system (w)? (∆E = q + w )

-----------------------------------------------------------------------------------------------------------------------------------------------e) Define state function (A state function is a function whose change depends on initial and final states but

not the path taken to go from initial to final.)

-----------------------------------------------------------------------------------------------------------------------------------------------f) The three symbols in the equation in d above (E, q, and w represent internal energy, heat, and work,

respectively. Why was internal energy written with a capital letter whereas the others were not? (E is a statefunction whereas q and w are not.)

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Xavier University of Louisiana 297

Chemistry 1020, Module 16

■Review From Module 6 (continued)1g) Why are state functions convenient to measure? (The values obtained can be compared without worrying

about the path taken in completing a process.)

-----------------------------------------------------------------------------------------------------------------------------------------------h) How can one measure the change in internal energy of a reaction? (Measure heat change at constant

volume.)

-----------------------------------------------------------------------------------------------------------------------------------------------i) While it is better to measure E than q or w for a system in the laboratory, measuring ∆E presents one major

problem? What is this problem? (∆E is heat change at a constant volume (i.e. in a closed container).Reactions carried out in a closed container can build up pressure and explode, a major disadvantagein a lab.)

-----------------------------------------------------------------------------------------------------------------------------------------------j) Because of the disadvantage of measuring ∆E mentioned above, chemists define a new thermodynamical

function, enthalpy. State the equation showing the relationship between enthalpy (H) and internal energy (E).(H = E + PV)

-----------------------------------------------------------------------------------------------------------------------------------------------k) Is enthalpy (H) a state function? (YES!!)

-----------------------------------------------------------------------------------------------------------------------------------------------l) How can one measure the change in enthalpy of a reaction? (Measure heat change at constant pressure–i.e.

measure heat change in an open container in a laboratory over a period of time when atmospheric pressure doesnot change appreciably.)

-----------------------------------------------------------------------------------------------------------------------------------------------m) To summarize, what are the two reasons why chemists find enthalpy changes convenient to measure in the

laboratory? (First, the pressure due to the atmosphere doesn't usually change a great deal during athree or four hour period Therefore, one can obtain ∆H by carrying out an experiment in an opencontainer in the lab. Second, enthalpy is a state function so enthalpy changes depend only upon initialand final conditions, not on the process by which a reaction is carried out. Thus, it is easy to comparevalues determined by different scientists.)

-1

------------------------------------------------------------------------------------------------------------------------------------------------2

-----------------------------------------------------------------------------------------------------------------------------------------------n) For some types of reactions, ∆H is approximately equal to ∆E. What is the primary characteristic of such

reactions? (There are no gaseous reactants or products.)

-----------------------------------------------------------------------------------------------------------------------------------------------o) What are standard conditions for thermodynamics? (1 molar concentrations, 1 atm pressure, and 25oC)

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298 Xavier University of Louisiana


■Review From Module 6 (continued)1p) State the three working rules which can be used when working with enthalpy changes. (First, the amount of

a substance which reacts or is produced is proportional to the enthalpy change in the equation.Second, the enthalpy change for a forward process is equal in magnitude and opposite in sign to theenthalpy change for the reverse reaction. i.e. ∆Hforward = -∆Hreverse. Third, Hess's Law: If anoverall equation can be obtained by combining steps in some manner, then the ∆H for the overallequation can be obtained by combining the ∆H’s for the steps in the same manner.) -1)

------------------------------------------------------------------------------------------------------------------------------------------------2)

------------------------------------------------------------------------------------------------------------------------------------------------3)

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■Review From Module 6 (continued)1q) Use Hess's Law to work each of the following problems. (Module 10)

S. 25 grams of ice at -13 oC is changed into steam at 115 oC.a) Draw a sketch breaking the overall process into parts. Then describe each of the parts.

0

100

sec

Co

-13

115❺

❶

❷

❸

❹❶The ice is heated from -13 oC to 0 oC.❷The ice is melted at 0 oC.❸The liquid water is heated from 0 oC to 100 oC.❹The liquid is vaporized from 100 oC.❺The steam is heated from 100 oC to 115 oC.

b) Calculate the heat change for the overall process.Calculate the ∆H for each of the steps in part a.❶heating ice = ∆H1 = Cice*amt*∆T = (2.092 J/goC)(25 g)(0oC - (-13oC) = 679.9 J❷melting ice = ∆H2 = ∆Hfus*amt = (6.02 kJ/mol)(25 g)(1 mol/18.0 g)(1000 J/1 kJ) = 8361 J

❸heating water = ∆H3 = Cwater*amt*∆T = (4.184 J/goC)(25 g)(100oC - 0oC) = 10460 J❹vaporizing = ∆H4 = ∆Hvap*amt = (40.67 kJ/mol)(25 g)(1 mol/18.0 g)(1000 J/1 kJ) = 56486 J

❺heating steam= ∆H5 = Csteam*amt*∆T = (1.841 J/goC)(25 g)(115oC - 100oC) = 690.4 JAdd all steps together to obtain ∆Hoverall .

∆H = ∆H1 + ∆H2 + ∆H3 + ∆H4 + ∆H5 = 679.9 J + 8361 J + 10460 J + 56486 J + 690.4 J =∆H = 76677 J = 76.677 kJ which rounds to 77 kJ using the rules of rounding for additionand subtraction. Remember, we were keeping an extra significant figure through thecalculations.

-----------------------------------------------------------------------------------------------------------------------------------------------A. 20 grams of water is heated from -10 oC to 85 oC at a constant pressure.

a) Draw a sketch breaking the overall process into parts. Then describe each of the parts.

b) Calculate the change in enthalpy for the process.




B. 30 grams of water is cooled from 115 oC to 25 oC at a constant pressure.a) Draw a sketch breaking the overall process into parts. Then describe each of the parts.


-----------------------------------------------------------------------------------------------------------------------------------------------C. 15 grams of water is heated from 35 oC to 140 oC at a constant pressure.






D. 50 grams of water is cooled from 125 oC to -5 oC at a constant pressure.a) Draw a sketch breaking the overall process into parts. Then describe each of the parts.


-----------------------------------------------------------------------------------------------------------------------------------------------E. 75 grams of water is cooled from 115 oC to -15 oC at a constant pressure.



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■Spontaneity, Factors Which Tend to Cause Reactions to Be Spontaneous, and Entropy2a) Define spontaneous reaction. (p. 784)

-----------------------------------------------------------------------------------------------------------------------------------------------b) The overall purpose of this module is to consider the question “Why are some reactions

spontaneous whereas others are not?” When first examining the question, it might appear that reactionsin which enthalpy (a kind of energy) decreases would be spontaneous–i.e., exothermic reactions would bespontaneous. Provide two examples of spontaneous exothermic reactions. (1. The dissolving of calciumchloride in water, one of the experiments you did in Chemistry 1011 Lab. 2. The freezing of liquidwater at –10 °C.)1)

2)

-----------------------------------------------------------------------------------------------------------------------------------------------c) The idea that all exothermic reactions are spontaneous (b above) was quickly discarded, however, because there

are many obvious exceptions–i.e, there are lots of spontaneous reactions which are endothermic. Provide twoexamples of a spontaneous chemical reaction which is endothermic. (1. The dissolving of ammonium nitratein water, one of the experiments you did in Chemisry 1011 Lab. 2. The vaporization of liquid waterinto steam above 100 °C.)1)

2)

-----------------------------------------------------------------------------------------------------------------------------------------------d) Eventually scientists determined that a decrease in enthalpy tends to make a reaction spontaneous but that there

is another “tendency” which must be considered before we can predict spontaneity. What is this secondtendency? (The tendency for systems to go to maximum randomness.)

-----------------------------------------------------------------------------------------------------------------------------------------------e) Define entropy (S). (Measure of the randomness of a system.)

-----------------------------------------------------------------------------------------------------------------------------------------------f) In the form of English used in the U.S., there are two other common ways of expressing the fact that something

is more random than another. What are they? (1) It is less ordered. 2) It is more disordered.)•1)

•2)



■Spontaneity, Factors Which Tend to Cause Reactions to Be Spontaneous, and Entropy (cont’d)2g) State the conditions under which the entropy of a substance is zero. (p. 799-800)

-----------------------------------------------------------------------------------------------------------------------------------------------h) State four kinds of common processes which occur with an increase in entropy and provide an example of each.

(1. When a substance changes from solid to liquid. 2. When a substance changes from liquid orsolid to gas. 3. When the number of particles increases from reactants to products. 4. When a soliddissolves in water)

Process for which entropy increases. Example•1)

•2)

•3)

•4)

i) If more than one of the processes in h above occurs, what dominates entropy change? (If more than one ofthe above occurs, whatever happens to the gases in the reaction will dominate.)

-----------------------------------------------------------------------------------------------------------------------------------------------j) Is entropy a state function? (YES!!)

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■The Laws of Thermodynamics3a) What is meant by the phrase “two systems are in thermal equilibrium?” (They are at the same

temperature.)

-----------------------------------------------------------------------------------------------------------------------------------------------b) State the Zeroth, First, Second, and Third Laws of Thermodynamics. (0th: If A is in thermal equilibrium

with B and B is in thermal equilibrium with C, then A and C are also in thermal equilibrium. 1st–General: The energy of the universe is constant. 1st–Chemists: Energy is neither created nordestroyed when a chemical reaction occurs. 2nd–General: The entropy of the universe is constantlyincreasing. 2nd–Chemists: A reaction which is spontaneous in one direction cannot be spontaneousin the opposite direction. 3rd: The entropy of a perfect crystal at 0 K is 0 .)

-Zeroth:

------------------------------------------------------------------------------------------------------------------------------------------------First (general form):

-First (as usually stated by chemists):

------------------------------------------------------------------------------------------------------------------------------------------------Second (general form):

-Second (as usually stated by chemists):

------------------------------------------------------------------------------------------------------------------------------------------------Third:

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■An Overview of the Relationship Between Spontaneity and Gibbs Free Energy4a) State the two general driving forces which tend to cause reactions to occur. (Systems tend to go to lowest

enthalpy and systems tend to go to the maximum randomness.)•1)

•2)

-----------------------------------------------------------------------------------------------------------------------------------------------b) Given the two general driving forces above, state the three reasons why a reaction might be spontaneous. (1.

Enthalpy decreases or 2) randomness increases or 3) both enthalpy decreases and randomnessincreases.)•1)

•2)

•3)

-----------------------------------------------------------------------------------------------------------------------------------------------c) We now know that there are two driving forces which tend to cause a reaction to occur and that we can explain

why a reaction is spontanous using one of the three reasons above. However, it would be easier to talk ofspontaneity if there were one function to which it is directly related. The function usually used for this purposeis called “Gibbs free energy.” Define Gibbs free energy (G). (p. 795)

-----------------------------------------------------------------------------------------------------------------------------------------------d) How is change in Gibbs free energy (∆G) for a reaction related to the reaction's change in entropy and enthalpy

at constant temperature? (p. 795)

-----------------------------------------------------------------------------------------------------------------------------------------------e) Explain how the sign of the free energy change is related to spontaneity. (p. 795)

•If ∆G < 0

•If ∆G > 0

•If ∆G = 0

-----------------------------------------------------------------------------------------------------------------------------------------------f) How is change in free energy related to work? (If free energy is negative, it is equal to the maximum

amount of work which could be derived from a spontaneous reaction. If it is positive, it is equal to theminimum amount of work which must be done to cause a nonspontaneous reaction to occur.)•If ∆G < 0

•If ∆G > 0

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✔✔✔■Predicting the Signs on Changes in Entropy, Enthalpy, and Free Energy for Reactions5a) Define the following six phase transitions among the three states of matter. State which are endo- and which are

exothermic. Transition | Definition | randomnness change? | Endo/Exo? • | | | | | | • | | | | | | • | | | | | | • | | | | | | • | | | | | | • | | | | | |

5b) S. a) Write the balanced chemical equation for the vaporization of water at 103 oC.H2O(liq) ➙ H2O(g) at 103 oC

b) Predict the signs for changes in entropy, enthalpy, and free energy for the reaction in a EXPLAINING HOW YOU OBTAIN YOUR ANSWER AS YOU DO SO by completing the following table. Change in | Its Sign |Explanation of how sign was obtained

Entropy | + | Liquid to gas transition occurs with an increase in randomness, | | i.e. entropy increases

Enthalpy | + | This is vaporization. We know that vaporization is endo- | | thermic, i.e. that ∆H is “+.”

Free Energy | - | Liquid water at 103 oC WOULD change into vapor since | | temp > bp. Therefore, the process is spontaneous & ∆G is “-.”

A. a) Write the balanced chemical equation for the vaporization of iodine at 100 oC. (The melting point ofiodine is 114 oC and the boiling point is 184 oC.)


Entropy | | | |

Enthalpy | | | |

Free Energy | | | |

B. a) Write the balanced chemical equation for the fusion of water at 10 oC.


Entropy | | | |

Enthalpy | | | |

Free Energy | | | |



✔✔✔■Predicting the Signs on Changes in Entropy, Enthalpy, and Free Energy for Reactions(continued)5b) C. a) Write the balanced chemical equation for the condensation of ethanol at 50 oC. (The boiling point of

ethanol is 76 oC and its melting point is -114 oC. Its formula is C2H5OH).


Entropy | | | |

Enthalpy | | | |

Free Energy | | | |

D. a) Write the balanced chemical equation for the crystallization of tin metal at 200 oC. (The melting pointof Sn is about 1000 oC.)


Entropy | | | |

Enthalpy | | | |

Free Energy | | | |

E. a) Write the balanced chemical equation for the condensation of nitrogen at 200 oC. .


Entropy | | | |

Enthalpy | | | |

Free Energy | | | |

F. a) Write the balanced chemical equation for the fusion of iodine at 50 oC. (The melting point ofiodine is 114 oC and the boiling point is 184 oC.)


Entropy | | | |

Enthalpy | | | |

Free Energy | | | |



✔✔✔■More Practice Predicting the Signs on Changes in Entropy, Enthalpy, and Free Energy6. S. a) Write the balanced chemical equation for the reaction of hydrogen and oxygen to form water at 25 oC.

The reaction is spontaneous at this temperature.2 H2(g) + O2(g) ➙ 2 H2O(liq)


Entropy | - | 3 moles gas become 2 moles of liquid so randomness | | decreases, i.e. entropy decreases

Enthalpy | - | Don’t know the sign of ∆H from common knowledge. Get it from | | ∆G = ∆H - T∆S; ∆H = ∆G + T∆S = (-) + (+)(-) = (-)*

Free Energy | - | Problem tells you that the reaction is spontaneous. Therefore, | | ∆G is “-.” •Or get ∆H from logic: Reactons occur because either a) ∆H is “-” or b) ∆S = “+” or c) both∆H = “-” and ∆S = “+” . This reaction is spontaneous but ∆S = “-” so situation “a)” must be true,i.e. ∆H = ‘-’ .

A. a) Write the balanced chemical equation for the combustion of CH4 (methane gas) to produce carbondioxide and water(liq). Both methane and carbon dioxide are gases at room temperature.


Entropy | | | |

Enthalpy | | | |

Free Energy | | | |

B. a) Write the balanced chemical equation for the spontaneous combustion of FeO(s) in O2(g) to produce

rust at 25 oC. "Rust" is Fe2O3(s).


Entropy | | | |

Enthalpy | | | |

Free Energy | | | |

C. a) Write the balanced chemical equation for the decomposition of table salt into its constituentelements at 25 oC.


Entropy | | | |

Enthalpy | | | |

Free Energy | | | |



✔✔✔■More Practice Predicting the Signs on Changes in Entropy, Enthalpy, and Free Energy(continued)6. D. a) Write the balanced chemical equation for the spontaneous reaction between HCl(g) and NH3(g) at

25 oC to produce ammonium chloride, a solid.

b) Predict the signs for changes in entropy, enthalpy, and free energy for the reaction in a EXPLAININGHOW YOU OBTAIN YOUR ANSWER AS YOU DO SO by completing the following table.

__________ Change in | Its Sign | Explanation of how sign was obtained

Entropy | | | |

Enthalpy | | | |

Free Energy | | | |

✔✔✔■Calculating Change in Free Energy from Changes in Entropy and Enthalpy7. Calculate change in free energy for the indicated reaction. (pp. 802-6)

S. a) The reaction CaCO3(s) ➙ CaO(s) + CO2(g) at 25 oC has a change in enthalpy of -66.1 kJ and achange in entropy of 160.7 J/K.

∆G = ∆H - T∆S

∆G = -66.1 kJ - (25 + 273 K)(160.7 J/K)( 1 kJ

1000 J) = -114.0 kJ

b) Is the reaction endothermic or exothermic? Explain how you know.Reaction is exothermic since ∆H is “-” .

c) Is the reaction spontaneous or nonspontaneous? Explain how you know.Reaction is spontaneous since ∆G is “-” .

-----------------------------------------------------------------------------------------------------------------------------------------------A. a) The reaction 2 KClO3(s) ➙ 2 KCl(s) + 3 O2(g) at 25 oC has an enthalpy change of -89.4 kcal and

a change in entropy of 118.2 cal/K.

b) Is the reaction endothermic or exothermic? Explain how you know.

c) Is the reaction spontaneous or nonspontaneous? Explain how you know.

-----------------------------------------------------------------------------------------------------------------------------------------------B. a) The reaction 2 Al(s) + 3 Cl2(g) ➙ 2 AlCl3(s) at 25 oC has an enthalpy change of -332 kJ and a

change in entropy of -93.4 J/K.



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✔✔✔■Calculating Change in Free Energy from Changes in Entropy and Enthalpy7. C a) The reaction P4O10(s) + 6 H2O(l) ➙ 4 H3PO4(s) has an enthalpy change of -416 kJ at 25 oC and an

entropy change of -209 J/K.



-----------------------------------------------------------------------------------------------------------------------------------------------D. a) The reaction 2 H2O2(l) ➙ 2 H2O(l) + O2(g) has an enthalpy change of -196 kcal at 25 oC and an

entropy change of 141 cal/K.



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E. a) The reaction 2 X + Y ➙ 3 Z has an enthalpy change of 122 kJ at 33 oC and an entropy change of -11.6 J/K.



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✔✔✔■Temperature Dependence of Spontaneity8a) What is an approximation for free energy change under the conditions indicated? (pp. 791-3) (At high

temperatures, ∆G ≈ -T*∆S. At low temperatures ∆G ≈ ∆H.)

-at high temperature? -at low temperature?

-----------------------------------------------------------------------------------------------------------------------------------------------b) S. For the exothermic reaction 2 Al(s) + 3 Cl2(g) ➙ 2 AlCl3(s),

•What is the sign on ∆H? Explain how you know.∆H = - since the problem says the reaction was exothermic.

•What is the sign on ∆S? Explain how you know.∆S = - since the balanced equation shows that gas is being transformed into solid, i.e. is

becoming more ordered.•What is the sign of T? Explain how you know.

T = + since ALL Kelvin temperatures are ≥0.

•How does temperature affect the spontaneity of the reaction?At low T: ∆G ≈ ∆H = - so reaction is spontaneous at low T.

At high T: ∆G ≈ -T∆S = -(+)(-) = -(-) = + so the reaction is NOT spontaneous at high T.

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8b) A. For the exothermic reaction N2(g) + 3 H2(g) ➙ 2 NH3(g),•What is the sign on ∆H? Explain how you know.

•What is the sign on ∆S? Explain how you know.

•What is the sign of T? Explain how you know.

•How does temperature affect the spontaneity of the reaction?

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B. For the reaction A (liq) ➙ A (vap),•What is the sign on ∆H? Explain how you know.




-----------------------------------------------------------------------------------------------------------------------------------------------C. For the exothermic reaction C6H12O6(s) + 6 O2(g) ➙ 6 CO2(g) + 6 H2O(l),

•What is the sign on ∆H? Explain how you know.




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✔✔✔■Temperature Dependence of Spontaneity (continued)8a) D. For the endothermic reaction A(g) + B(g) ➙ 2 C(s) + D(g),





-----------------------------------------------------------------------------------------------------------------------------------------------E. For the exothermic reaction A(s) + B(g) ➙ C(g) + D(g),





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✔✔✔■Relationship Between Standard Free Energy and Cell Potentials9a) In previous portions of this handbook, you have learned that both the voltage produced by a cell under standard

conditions (Eo) and the standard free energy change (∆Go) are related to the spontaneity of a reaction. Forexample, in Module 17 you learned that reactions in cells with Eo>0 were spontaneous and in Learning Goal #4above, you learned that those with ∆Go<0 were spontaneous. Therefore, it is probably obvious that Eo isrelated to ∆Go for the reaction on which the cell is based. What is the equation which relates the two ? Defineall terms in the equation.

-----------------------------------------------------------------------------------------------------------------------------------------------b) Calculate the voltage and free energy change for the following cell at standard conditions. (pp. 810-4)

S. Zn(s)|Zn2+||Cu2+|Cu(s)Zn(s) ➙ Zn2+ + 2 e- , Eo = 0.76 volts ∆Go = -nFEo

Cu2+ + 2 e- ➙ Cu(s) , Eo = 0.34 volts ∆Go = -(2mol e-)(96500 coul)(1.10 V)(1J/coul1 volt )=

mol e-

Zn(s) + Cu2+ ➙ Zn2+ + Cu(s), Eo = 1.10 volts = -2.123*105 Jwhich rounds to∆Go = -2.12*102 kJ

n = # electrons transferred = 21 volt = 1 J/1 coul

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✔✔✔■Relationship Between Standard Free Energy and Cell Potentials (continued)9b) Calculate the voltage and free energy change for the following cell at standard conditions. (pp. 848-51)

A. Cd(s)|Cd2+||Cu2+|Cu(s)

-----------------------------------------------------------------------------------------------------------------------------------------------B. Ni(s)|Ni2+||Zn2+|Zn(s)

-----------------------------------------------------------------------------------------------------------------------------------------------C. Zn(s)|Zn2+||Ag+|Ag(s)

-----------------------------------------------------------------------------------------------------------------------------------------------D. Co(s)|Co2+||Fe2+|Fe(s)

-----------------------------------------------------------------------------------------------------------------------------------------------E. Ni(s)|Ni2+||Co2+|Co(s)

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✔✔✔■Relationship Between Standard Free Energy and Equilibrium Constant10a) The standard free energy associated with a given reaction can rather easily be shown to be related to the

equilibrium constant for the reaction. Therefore, it is not necessary to measure both. Instead, you can measureone and then calculate the other from it. (Or you can measure voltage for a cell based on the reaction understandard conditions and calculate both from Eo as indicated in Learning Goal #9 above and Learning Goal #8 inModule 17.) What is the equation which relates ∆Go and K.•in exponential form? •in log form?

Define all terms in the equations.-----------------------------------------------------------------------------------------------------------------------------------------------

b) S. The standard free energy change for a certain reaction is -180 cal/mol. What is the equilibrium constant forthe reaction at 25 oC? (pp. 810-4)

∆Go = -180 cal/mol (4.184 J

1 cal ) = -753 J/mol K = 10-∆G°/(2.303RT))

R = 8.314 J/mol*K K = 10-(-753 J/mol)/(2.303)(8.314 J/mol K)(298 K) =T = (25 + 273 K) = 298 K K = 100.132

K = 1.36

-----------------------------------------------------------------------------------------------------------------------------------------------A. The standard free energy change for a certain reaction is 340 J/mol. What is the equilibrium constant for the

reaction at 25 oC?

-----------------------------------------------------------------------------------------------------------------------------------------------B. The standard free energy change for a certain reaction is 389 cal/mol. What is the equilibrium constant for

the reaction at 25 oC?

-----------------------------------------------------------------------------------------------------------------------------------------------C. The standard free energy change for a certain reaction is -487 J/mol. What is the equilibrium constant for

the reaction at 25 oC?

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✔✔✔■Relationship Between Standard Free Energy and Equilibrium Constant (continued)10b) D. The standard free energy change for the reaction of A + 2 B ➙ C is 55 cal/mol. What is the equilibrium

constant for this reaction at 300 oC?

-----------------------------------------------------------------------------------------------------------------------------------------------E. The standard free energy change for a certain reaction is -67.2 cal/mol. What is the equilibrium

constant for this reaction at 212 oC?

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10c) S. Water undergoes autoionization according to the reaction H2O(aq) = H+(aq) + OH-(aq). The

equilibrium constant for this process at 25 oC is 1.0*10-14. What is the standard free energy change for theprocess? (p. 810-4)K = 1.0*10-14 ∆Go = -2.303*R*T*log KT = (25 + 273 K) = 298 K

R = 8.314 J/mol*K ∆Go = -2.303(8.314J

mol*K)(298 K)(log 1.0*10-14) kJ

1000J

R∆Go = 79.8818 kJ/mol = 8.0*101 kJ/mol

-----------------------------------------------------------------------------------------------------------------------------------------------A. What is the standard free energy change for the dissociation of nitrous acid in water at 25 oC?

-----------------------------------------------------------------------------------------------------------------------------------------------B. What is the standard free energy change for the dissociation of formic acid in water at 25 oC?

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✔✔✔■Relationship Between Standard Free Energy and Equilibrium Constant (continued)10c) C. What is the standard free energy change for the dissociation of acetic acid?

----------------------------------------------------------------------------------------------------------------------------------------------- D. What is the standard free energy change for the dissolving of CuS in water?

-----------------------------------------------------------------------------------------------------------------------------------------------E. What is the standard free energy change for the dissolving of Ag2S in water?

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■Bonding/Model Act iv i ty to Improve Abi l i ty to Visual ize in 3-DA. a) Write a balanced equation if methylamine (CH3NH2) is placed in water.

b) Draw the Lewis structure of all of the species in the above two reactions.

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■Bonding/Model Activi ty to Improve Abil i ty to Visualize in 3-D (continued)B. a) Write a balanced equation if ethylamine (CH3CH2NH2) is placed in water.


-----------------------------------------------------------------------------------------------------------------------------------------------C. a) Write a balanced equation if hypochlorous acid is placed in water.


-----------------------------------------------------------------------------------------------------------------------------------------------D. a) Write a balanced equation if nitrous acid is placed in water.


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A-D c) When you go to drill be prepared to assemble models of each of the reactants in the equations above andthen use those models to demonstrate to your instructor what happens as the reactions occur.



■Challenge Questions

A. Draw a diagram indicating the relationship between the entropy and the temperature as a piece of ice at -10 oC isheated to 120 oC.

B. Since you previously learned that both heat of vaporization and boiling point increase as intermolecular forces ina substance increases, it is not surprising to learn that there is a quantitative relationship between the twovariables. Use the data in the table below to determine what that relationship is making certain that you use allof the data.

Enthalpy of Vaporization (kJ/mole) tbBenzene 30.8 80.2 oCEther 26.0 34.6 oCMethane 10.4 -164.0 oC

C. The reaction A + B ➙ C proceeds at room temperature with an enthalpy change of 23 kJ/mole and entropychange of -10 J/K. Under similar conditions, C reacts with D to produce E with an enthalpy change of-40 kJ/mole and an entropy change of 15 J/K. Does the overall reaction, A + B + D ➙ E, proceed

spontaneously at room temperature (25 oC)? Show all your reasoning and mathematics.

D. The reaction A + B ➙ C proceeds at room temperature with an enthalpy change of -23 kJ/mole and entropychange of 10 J/K. Under similar conditions, C reacts with D to produce E with an enthalpy change of -40kJ/mole and an entropy change of -15 J/K. Does the overall reaction, A + B + D ➙ E, proceed

spontaneously at room temperature (25 oC)? Show all your reasoning and mathematics.

E. If ∆H = 42.6 kJ/mol for C2H5OH(liq) ➙ C2H5OH(g) and ∆S for the process is 121.6 J/mol*K, what is thenormal boiling point for ethanol, C2H5OH?

F. If ∆H for a reaction is +36.7 kJ/mol and ∆S is +201 J/mol*K, what is the lowest temperature at which thisreaction will be spontaneous?

Revised: Donna Howell, Spr 2000; Mike Adams, Spr 2001; RBSK Spr 2003.


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Study Guide for Module 16—Thermodynamics · Study Guide for Module 16—Thermodynamics ... Reading Assignment: Chapter 16 in Chemistry, 6th Edition by Zumdahl. Guide for Your Lecturer: