Spontaneous, non-spontaneous, reversible, irreversible, entropy, Gibb's free energy,

Concept checklist:
1. Give examples and define each of the following, Spontaneous, non-spontaneous, reversible, irreversible processes
2. Know the conditions that would increase the entropy of a system.
3. Explain the 2nd and 3rd law of thermodynamics using simple language.
4. Be able to calculate Gibbs free energy by three different methods.
5. Be able to calculate Gibbs free energy under non-standard conditions.

Problems:

1. Criticize the following statements: a) The entropy of all spontaneous reactions increases. b) A reaction with a negative free energy change (G<0) is predicted to be spontaneous with rapid transformation between reactants and products. c) All spontaneous reactions are exothermic d) Endothermic reactions are never spontaneous.
2. Tell which substances has a higher entropy is each of the following pairs: a)A sample of pure Si or a piece of Si containing a trace of some other atoms such as B or P, used in computer chips. b) An ice cube or liquid water, both at 0°C. c) A sample of pure solid I₂, or iodine vapor, both at 298 K.
3. Calculate the entropy change  S° for each of the following changes and comment on the sign of each change. a) NH_3(g) ¦ NH_3(aq) b) Na_(g) ¦ Na_(s) c) CCl_4(g) ¦ CCl_4(l)
4. Calculate the standard molar entropy change for the formation of each of the following compounds from elements at 25 °C. a) H₂O_(l) b) MgO_(s) c) CaF_2(s) d) Al₂O₃
5. Using values of H, S, calculate G° for each of the following reactions: a)Pb_(s) + Br_2(g) --> PbBr_2(s) b) Mg_(s) + ½ O_2(g) ¦ MgO_(s) c) NH_3(g) + HCl_(g) ¦ NH₄Cl_(s) Which of the values of G that you just calculated correspond to a G_f? In those cases, compare your value to the literature value. Which of these reactions are spontaneous at 298 K?
6. Write a balanced chemical equation that depicts the formation of 1 mol of Fe₂O_3(s) from its elements. What is the free energy of formation of 1.00 mol of Fe₂O_3(s)? What is the standard free energy change when 1 pound of Fe₂O_3(s) is formed from its elements?
7. If gaseous hydrogen can be produced cheaply, it can be burned directly as a fuel or converted to another fuel, methane (CH₄): 3H_2(g) + CO_(g) ¦ CH_4(g) + H₂O_(g). Calculate H, S and G (by two methods) for this reaction at 298 K. Is it spontaneous?
8. The dissociation of chlorine molecules in chlorine atoms has an equilibrium constant of 0.106 at 1800K. Cl_2(g) ¦ 2Cl_(g) Calculate the G for the reaction at this temperature.
9. For each of the following processes, give the algebraic signs of H, S, and G. No calculations are needed, use your common sense. a) Splitting of liquid water to give gas phase oxygen and hydrogen, a process that requires lots of E. b) dissolving a small amount of NH₄Cl in water. The solution become quite cold. c) The explosion of dynamite, a mixture of nitroglycerin (C₃H₅N₃O₉) and diatomaceous earth. The explosive decomposition gives gaseous products such as water, CO₂ and other. Lots-o-Heat. d) The combustion of gasoline in the engine of your car, mostly octane by

C₈H_18(g) + 25 O_2(g) ¦ 16 CO_2(g) + 18 H₂O_(g) + heat

10. The equilibrium constant K_p for N₂O_4(g)<--> 2 NO_2(g) is 0.15 atm at 298 K. Calculate G° from this constant, and compare your calculated ∆G rxn with that calculated from literature values of G_f.
11. A crucial reaction for the production of synthetic fuels is the conversion of coal to H₂ with steam: C_(s) + H₂O_(g)¦ CO_(g) + H_2(g). a) calculate G° for this reaction by two different methods at 298K, assuming C_(s) is graphite. b) Calculate K_p for this reaction. c) Is this reaction spontaneous under standard conditions. If not, is there a temperature at which it becomes spontaneous? d) At what T will K_p = 1.0 x 10^-4?
12. Calculate  G° for the decomposition of sulfur trioxide into sulfur dioxide and oxygen. Is the reaction spontaneous? If no, at what temperature will it be spontaneous? What is the equilibrium constant at 1500 °C?

Some other 'hints': 

WN 03 OTE 19:

1. (12) Hey this question looks familiar… a) Express the second law of thermodynamics in words. b) If the entropy of a system increases during a reversible process, what can you say about the entropy change of the surroundings? c) In a certain spontaneous process, the system undergoes an entropy change (S) of 42 J/K. What can be said about the sign and magnitude of S_surround?
2. (12) The normal freezing point of 1-propanol is –127 °C. a) Is the freezing of 1-propanol endothermic or exothermic? How do you know? b) In what temperature range is the freezing of 1-propanol spontaneous? Explain your answer. c) What is a reversible process? d) Is there a temperature in which the freezing of 1-propanol is a reversible process?
3. (16) For the following reaction, calculate G°_rxn at 25.00 °C by two different methods.

1 SO_2(g) + 2 H_2(g) ¦ 1 S_(s) + 2 H₂O_(g)

Chapter 20

Define the following:

Oxidation, reduction, oxidizing agent, reducing agent, voltaic cell, galvanic cell, anode, cathode, electromotive force, cell potential, standard reduction potential, battery, electrolysis, corrosion

Unit Objectives:

1. Recognize oxidation-reduction reactions, and label each species

2. Balance oxidation-reaction reactions in neutral solutions, acid solutions, and base solutions

3. Be able to explain all the parts of a voltaic cell.

4. Know the units of cell EMF and how to calculate it using standard potentials

5. Be able to rank species by activity.

6. Understand the relationship between del G and cell emf. Do appropriate calculations.

7. Understand the relationship between solution concentration and cell emf. Do appropriate calculations.

8. Define the mains pieces of a battery

9. Understand electrolysis and do appropriate calculations.

Problems:

Chapter 20: 3,5,7,9,11,13,21,23,29,31,37,43,47,49,57,59,61,63,95,105

Here is one behemoth question, that is a legit exam question. This question must be solved in order, otherwise, it doesn't work.

Consider the REDOX reaction 1 Fe⁺²_(aq) + 1 Ag⁺¹_(aq) ¦1Fe⁺³_(aq) + 1 Ag_(s)   
1. Calculate the E°_cell of this reaction
2. As the reaction proceeds, what happens to the concentration of each ion in system? (increase, decrease, or stay the same?)
3. As as we eek away from standard conditions, what will happen to the Ecell?
4. Calculate the ΔG° of this reaction.
5. Calculate Ksp of this reaction.
6. The following are standard entropies of reaction of Fe⁺³_(aq) , Ag⁺¹_(aq) , and Fe⁺²_(aq) , respectively are , -315.9 J/K, 72.7 J/K and -137.7 J/K. Calculate the ΔS° for this reaction.
7. Calculate ΔH° for the reaction.
8. This reaction is spontaneous at 298 K. Is there a temperature range at which it would not be spontaneous?
9. Compare your results from question #8 and #3. Comment on the implications of each and how they relate.

Some other 'hints': 
- Balance lots of half reactions for practice.

- There MIGHT be an explain to your nephew question.

- The concept is the most important part. The method is next, and then comes the answer.

CEM 142 WN03 Mega-Quiz 20

1. (14) I have an acidic solution that contains VO₂⁺¹_(aq) ion. Into this solution I bubble some NO_(g). A REDOX reaction occurs. The two products are VO⁺²_(aq) and NO₃^-1_(aq).
a. Write the two half reactions (COMPLETE) remember this reaction is occurring in an acidic sol’n.
b. Write the complete net reaction (you better make sure it is all balanced)
2. (14) A thought problem. Beaker ♣: 3.0 M Al⁺³_(aq). Beaker ♥: 0.2 M Al⁺³_(aq). I take these two beakers and put ONE piece of Al_(s) wire and ‘connect’ the beakers. Nothing happens. Oh yeah, I forgot that pesky salt-bridge thingie. Ok, so I add a salt bridge and something happens.
a. Explain (in detail, give reactions) what occurs in beaker ♣.
b. Explain (in detail, give reactions) what occurs in beaker ♥.
c. What happens to the total mass of the Al wire? Explain.

3.(14) Here, have some reduction potentials:
AuBr₄^-1_(aq) + 3 e^---> Au_(s) + 4 Br^-1_(aq)  E^◦_red = -0.858 V
Eu⁺³_(aq) + 1 e^- --> Eu⁺²_(aq)  E^◦_red = -0.430 V
IO^-1_(aq) +1 H₂O_(l) + 2 e^- --> 2 OH^-1_(aq) +  I^-1_(aq)  E^◦_red = +0.490 V
Sn⁺²_(aq) + 2 e^- --> Sn_(s)   E^◦_red = -0.140 V
a. Write the cell reaction for the combination of these half cell reactions that leads to the largest positive cell potential, and calculate said potential.
b. Be detailed (and complete) how you would set up such a cell that gives EXACTLY that potential. A picture is fine, just make sure you have everything you need.
c. Let us say that you want a cell potential that is slightly higher than you calculated in part a. Describe (in words only) what you could do to your setup in part b to accomplish said elevation of cell potential.

Chapter 21

Concept checklist:
1. Recognize and balance nuclear equations
2. Define and explain all five kinds of radioactive activity discussed in class
3. Explain the band of stability and why it has the shape that it does.
4. Explain what a radioactive series is.
5. Give properties of 'stable' nuclear configurations
6. Explain what nuclear transmutation is and how it is done.
7. Explain and predict and calculate nuclear decay rates.
8. Give some practical uses of nuclear chemistry
9. Explain what is meant by mass defect and how it relates to nuclear energy
10. Calculate nuclear binding energy
11. Explain the pieces of a nuclear reactor
12. Explain the major pieces of a nuclear explosive
13. Define and explain nuclear fusion
14. Discuss the biological effects of radiation and understand the differences between units of measuring radiation.

Problems for chapter 21: 1,4,7,11,17,21,23,29,37,43,47,51,63,74

Some other 'hints': 
-There will most likely be another 'explain this concept to your 8th grade nephew' questions. 
- There will probably be two calculations. Remember, ENERGY is not created or destroyed, by mass can be.
- The concept is the most important part. The method is next, and then comes the answer.

CEM 152 WN 03 Mega-Quiz 21          G º =H - TS
1. (16) Give the four major pieces of a nuclear power plant. Define the role of each, give examples.
2. (12) Time to talk to your 5^th grade nephew again. He comes to you and says “My science teacher says there is enough energy in a glass of water to power the city for a week” Your nephew understands the structure of the atom (protons, neutrons and such) but wants you to explain why fusion is so great, and why we can’t use it? Remember, use small words.
3. (12) Einsteinium-253 (Es, element 99) was first discovered after the first full scale Hydrogen bomb test in December of 1952. It being larger than Uranium, it is unstable and has a half life of only 20.4 days. There are 5 forms of radioactive activity talked about in class. Give complete nuclear equations showing 4 of these activities using Es-253.
4. (10) Consider the following reaction and statistics:
C₂H_6(g) --> C₂H_4(g) + H_2(g) H^◦ = 137 kJ ; S^◦ =120 J/K
Explain in detail under what conditions this reaction is spontaneous, non-spontaneous, and reversible. Be complete, do not just give the numbers.
 

Chapter 25:

Last Updated 9Apr03