problems

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1. Which statement is FALSE? a) If a reaction is thermodynamically spontaneous, it may occur rapidly. b) A fast reaction may be thermodynamically spontaneous. c) If a reaction is thermodynamically spontaneous, it may occur slowly. d) If a reaction is thermodynamically spontaneous, it must have a low activation energy. e) Rate of reaction is a kinetic quantity rather than a thermodynamic quantity. 4. What is the entropy change of the reaction below at 298K and 1 atm pressure? N 2 (g) + 3H 2 (g) ----> 2NH 3 (g) S(J/mol x K) 191.5 130.6 192.3 a) -198.7 J/K b) 76.32 J/K c) -129.7 J/K d) 303.2 J/K e) 384.7 J/K 5. If the entropy change for the reaction below at 298 K and 1 atm pressure is 137 J/K, and S=205 J/mol x K for O 2 (g), what is S for O 3 (g)? 2O 3 ----> 3O 2 a) 364 J/mol x K b) 478 J/mol x K c) 239 J/mol x K d) -117 J/mol x K e) -59 J/mol x K 1

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Page 1: Problems

1. Which statement is FALSE?a) If a reaction is thermodynamically spontaneous, it may occur rapidly.b) A fast reaction may be thermodynamically spontaneous.c) If a reaction is thermodynamically spontaneous, it may occur slowly.d) If a reaction is thermodynamically spontaneous, it must have a low activation energy.e) Rate of reaction is a kinetic quantity rather than a thermodynamic quantity.

4. What is the entropy change of the reaction below at 298K and 1 atm pressure? N2(g) + 3H2(g) ----> 2NH3(g)S(J/mol x K) 191.5 130.6 192.3a) -198.7 J/K b) 76.32 J/K c) -129.7 J/K d) 303.2 J/K e) 384.7 J/K

5. If the entropy change for the reaction below at 298 K and 1 atm pressure is 137 J/K, and S=205 J/mol x K for O2(g), what is S for O3(g)? 2O3 ----> 3O2

a) 364 J/mol x K b) 478 J/mol x K c) 239 J/mol x K d) -117 J/mol x K e) -59 J/mol x K

6. The heat of vaporization of methanol, CH3OH, is 35.20 kJ/mol. Its boiling point is 64.6 degrees Celsius. What is the change in entropy for the vaporization of methanol?a) -17.0 J/mol x K b) 3.25 J/mol x K c) 17.0 J/mol x Kd) 104 J/mol x K e) 543 J/mol x K

7. Which one on the following reactions has a positive entropy change?a) H2O(g) ----> H20(l)b) BF3(g) + NH3(g) ----> F3BNH3(s)c) 2SO2(g) + O2(g) ----> 2SO3(g)d) N2(g) + 3H2(g) ----> 2NH3(g)e) 2NH4NO3(s) ----> 2N2(g) + 4H2O(g) + O2(g)

8. Based on the relationship of entropy to the degree of disorder in a system, which response includes all of the following changes that represent an increase in entropy, and no others?

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I. the freezing of water II. the condensation of steamIII. sublimation (vaporization) of dry ice, solid CO2

IV The evaporation of CCl4.a) I and IV b) II and IV c) I and II d) III and IV

9. Which response contains all the processes below that occur with an increase in entropy and no others?I. The evaporation of CCl4.II. The precipitation of white silver chloride, AgCl, from a solution containing silver ions and chloride ionsIII. The reaction PCl3(g) + Cl2(g) ----> PCl5(g)IV. Thirty-five pennies are removed from a bag and all are placed heads up on a table.a) I b) II and IV c) I, III, and IV d) II and IIIe) another one or another combination

10. Consider the conversion of a substance from solid to liquid.Solid<===> Liquid

At one atmosphere pressure and at the melting point of the substance, a) Δ H = 0 for the process b) Δ S = 0 for the processc) Δ G is less than 0 for the process d) Δ G = 0 for the processe) both Δ H and Δ S = 0 for the process

11. What is Δ G for the reaction below at 25 degrees C?2C2H2(g) + 5O2(g) ----> 4CO2(g) + 2H2O(l)

Values for Δ Gf for the reactants and products in the above order (in kJ/mole) are: 209.2, 0, -394.4, -237.2a) -1409 kJ b) -2599 kJ c) -1643 kJ d) -2470 kJ e) -766 kJ

12. Calculate Δ Gf at 298K for PbCl2(s) from the following information. Δ G° for the reaction below is -58.4kJ at 298K. PbS(s) + 2HCl(g) ----> PbCl2(s) + H2S(g)Δ Gf (kJ/mol) -98.7 -95.3 ? -33.6 a) -16.0 kJ/mol b) -47.6 kJ/mol c) -314.1 kJ/mol d) -36.2 kJ/mol e) -52.3 kJ/mol

13. For the following reaction at 298K, Δ H = -26.88kJ and Δ S = 11.2

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J/K. Calculate Δ G for the reaction.I2(g) + Cl2(g) ----> 2ICl(g)

a) -102 kJ b) 50.6 kJ c) -30.2 kJ d) -50.6 kJ e) -77 kJ

14. Estimate the temperature at which Δ G = 0 for the following reaction.NH3(g) + HCl(g) ----> NH4Cl(s)

For the reaction, ΔH = -176 kJ, and Δ S = -284.5 J/K a) 467K b) 582K c) 619K d) 634K e) 680K

15. Estimate the boiling point of hydrogen peroxide, H2O2. The heat of vaporization for H2O2 is 51.5 kJ/mole and the entropy of vaporization is 123.4 J/K mole. a) 67.6 degrees C b) 144 degrees C c) 26.2 degrees Cd) -11.4 degrees C e) 118 degrees C

16. A process CANNOT be spontaneous ifa) it is exothermic, and there is an increase in disorderb) it is endothermic, and there is an increase in disorderc) it is exothermic, and there is a decrease in disorderd) it is endothermic, and there is a decrease in disorder

17. Which of the following statements is NOT correct?a) When Δ G for a reaction is negative, the reaction is spontaneousb) When Δ G for a reaction is positive, the reaction is nonspontaneousc) When Δ G for a reaction is zero, the reaction is spontaneousd) When Δ H for a reaction is negative, the reaction is never spontaneouse) When Δ H for a reaction is VERY positive, the reaction is not expected to be spontaneous

18. Which statement below is FALSE?a) For reactions that release heat to the surroundings, Δ H is negativeb) For reactions in which the reacting system becomes more disordered, Δ S is positive.c) If the free energy change of reaction is positive, the reaction cannot occur to give predominantly products under the given conditions.d) The entropy of a system increases when order increasese) Endothermic reactions may be spontaneous

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19. For the reaction given below at 25 degrees C, Δ H = -1516kJ and Δ S = -432J/K. This reaction is spontaneous _____

SiH4(g) + 2O2(g) ----> SiO2(s) + 2H2O(l)a) only below a certain temperatureb) only above a certain temperaturec) at all temperatures d) at no temperaturee) cannot tell from the information available

20. Consider the following reaction NH4Br(s) ----> NH3(g) + HBr (g) The Δ H for the reaction is +188kJ Which response describes the thermodynamic spontaneity of the reaction? a) The reaction is spontaneous at all temperatures b) The reaction is spontaneous only at relatively high temperatures c) The reaction is spontaneous only at relatively low temperatures d) The reaction is not spontaneous at any temperatures e) We cannot tell from the information given

21. At 25 degrees C,ΔH = 128.9 kJ and Δ S = 320 J/K for a reaction. Above what minimum temperature will this reaction become spontaneous? a) 298K b) 332K c) 403K d) 530K e) 1150K----------Key---------- 1. (d) 4. (a) 5. (c) 6. (d) 7. (e) 8. (d) 9. (a) 10. (d) 11. (d) 12. (c) 13. (c) 14. (c) 15. (b) 16. (d) 17. (d) 18. (d) 19. (a) 20. (b) 21. (c)

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ANSWER THE FOLLOWING QUESTIONS:1.Using G to predict the direction of a reaction If G < 0 then reaction proceeds to the ________ If G > 0 then reaction proceeds to the ________ If G = 0 then reaction as is ________ ________

2.The heat of vaporization of mercury is 60.7 kJ/mol. For Hg(l) , So = 76.1 J/K-mol and for Hg(g) So = 175 J/K-mol. Calculate the temperature at which the phase change occurs.

3.At constant temperature and pressure, a chemical change can only be spontaneous if it is accompanied by a ________ in the free energy of the system.

If G for a reaction is ________, reaction will occur spontaneously.

If G for a reaction is ________, reaction will not occur spontaneously.

H negative, S positive, reaction ________ at all temperatures H positive, S negative, reaction ________ at all temperatures H positive S positive, reaction spontaneous at _____ _____ H negative S negative, reaction spontaneous at ____ _____

4.At absolute zero the entropy of a perfectly ordered pure crystalline substance is ________.

5.This means that, unlike energy, we can know by experimental measurement the total ________ of a system.

6.Standard entropy is defined as the entropy of a substance at ________ and ________ of pressure.

7. Molecular complexity – when a reaction occurs with a decrease in the molecular complexity and an increase in the number of particles, there tends to be an ________ in entropy.

8.Predict the sign of S for the following reactions: 2SO2(s) + O2(g) 2SO3(g)

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CO(g) + 2H2(g) CH3OH(l) Ca(OH)2(s) Ca2+(aq) + 2OH-(aq) 2NO2(g) N2O4(g) Hg(l) Hg(g)

9.Whenever a spontaneous event takes place in our universe, it is accompanied by an overall ________ in entropy

10. Temperature – increasing the temperature ________ the entropy of a system

11.Physical states and phase changes – when a ________ ordered phase changes to a ________ ordered one (solid to liquid or liquid to gas) there is an increase in entropy

12.Dissolution of a solid or liquid – the entropy of a dissolved solid or liquid is usually________ than the entropy of the pure solute

13.Dissolution of a gas – gas is very disordered to begin with; dissolution usually results in a ________ in entropy.

14.Entropy is the thermodynamic quantity that describes the ________ of a system.

15.Thermodynamics is the study of the laws that govern the ________ and ________ changes of physical and chemical events

16.First Law of Thermodynamics (law of conservation of energy) states that the energy of the universe is _______ and can be transferred or transformed but neither ________ nor.

17. Energy is a ________ ________, meaning that it depends only upon the initial and final states and not upon the path taken between the two states.

18. A ________ reaction is one that occurs without outside assistance

19.Calculate the change in entropy for the vaporization of 150.0g of

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bromine liquid. Br2(l) --> Br2(g) So (Br2l) = 152.3J/mol-K and So (Br2g) = 245.3J/mol-K

20.Is the absorption of 1000kJ of heat and an increase in disorder of 5.00 kJ/K a spontaneous process at 300 K?

21.In a reaction where entropy decreases, it is found that the reaction has a positive Δ G, but becomes spontaneous as the temperature decreases. Which of the following is true?

(A)Δ S and Δ H are both positive(B)ΔS and Δ H are both negative(C)ΔS is negative and Δ H is positive(D)ΔS is positive and Δ H is negative(E) Δ S and Δ G are both equal to zero

21.Which of the following statements is true of a reaction that is spontaneous at a given temperature that then becomes non- spontaneous at a higher temperature? (A) Δ S and Δ H are both positive (B) Δ S and Δ H are both negative (C) Δ S is negative and Δ H is positive (D) Δ S is positive and Δ H is negative (E) Δ S and Δ G are both equal to zero

22.Which of the following terms must be negative, in reactions that are spontaneous (feasible)? (A) Δ H (B) Δ S (C) Δ G (D) Temperature

23.When burning a solid hydrocarbon, which set of values would be most likely? (A) Negative Δ H, NegativeΔS, Negative Δ G (B) Negative Δ H, Negative Δ S, Positive Δ G (C) Negative Δ H, Positive Δ S, Negative Δ G (D) Positive Δ H, Negative Δ S, Negative Δ G (E) None of the above24.What are the signs of Δ H and Δ S for a reaction that is spontaneous at all temperatures?

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(A) Δ H positive, Δ S negative (B) Δ H positive, Δ S positive (C) Δ H negative, Δ S positive (D) Δ H negative, Δ S negative (E) None of the above25.Consider the decomposition of solid Calcium carbonate to give Carbon dioxide gas and solid Calcium oxide. What can be deduced about the change in entropy in this reaction? (A)Nothing (B) Δ S = 0 (C) Δ S is positive (D) Δ S is negative (E) None of the above

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ANSWER THE FOLLOWING QUESTIONS:1.Which of the following statement is true about thermodynamics.

a) Thermodynamics will help in predicting whether a physical or chemical change is possible under given conditions.

b) Thermodynamics only deals with the initial and final states of the system and is not helpful in evolving the mechanism of the process.

c) The rate of a reaction can be evolved from thermodynamics.d) The mechanism of a reaction can be evolved from thermodynamics. 1) a only 2) a & b 3) a, b & c 4) a & d

2. Choose the incorrect statementa) Open systems can exchange both energy and matter with its surroundings.b) Closed systems can only exchange energy and do not exchange matter with its surroundings.c) Isolated systems can exchange energy and matter with its surroundings .d) None.

1. The enthalpy change of solution formation for KBr in water is +19.8 kJ/mol. However, the solubility of KBr is very high in water. This is due to:

a) a higher entropy (disorder) in solution compared to the solid. b) an exothermic solvation process. c) solvent-solvent interactions. d) an endothermic solvation process.

4. The thermodynamically expression for change in entropy is given by 1) qrev/T 2) qirrev/T 3) w+q/T 4) Wirrev/T

5. Consider the following statements about entropy . a) An ideal gas occupying larger volume has higher entropy than when it occupies smaller volume under given conditions. b) The gases with higher atomic or molecular weights possess greater entropy values. c) The change in entropy of an ideal gas in isothermal free expansion is always negative.e) The molar entropy of a dilute solution is greater than that of concentrated

solution.f) Solids possess very high entropy values than liquids and gases. The correct

Answer is 1) c and e 2) a, c and d 3) a, b and c 4) b, c and e

6. Which of the following is the significance of third law of thermodynamics. a) The absolute entropy of a substance decreases with increasing temperature. b) The change in entropy of the universe must be positive for a spontaneous process. c) The absolute value of entropy can be measured for some very pure substances. d) The entropy of the universe is constant.

7. For which one of the following reactions does the entropy of the system increase.

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a) NH3(g) + HCl(g) NH4Cl(s) b) 2H2(g) + O2(g) 2H2O(g)

c) NH3(g) + H2O(l) NH4+

(aq) + OH-(aq) d) 2H2O2(l) 2H2O(l) + O2(g)

8. Which of the following statements best describes the spontaneity of a reaction at 25oC for which Ssys is negative and Ssurr is positive .? a) The reaction cannot be spontaneous at 25oC. b) The reaction will be spontaneous at all temperatures.c) The reaction will be spontaneous only if Ssys is greater in magnitude than Ssurr.d) The reaction will be spontaneous only if Ssurr is greater in magnitude than Ssys.

9. Which of the following quantities can be determined directly from the slope of a ln P versus l/T representation ?

a) Equilibrium constant. b) Molar volume in gas phase. c) Temperature of boiling d) Enthalpy of vaporization

10. The term – TΔ Suniv at constant temperature and pressure is known as a) Gibbs function b) Helmholtz function c) Entropy function d) All

11. Which of the following is incorrect for a reaction A B ? a) The reaction can spontaneously proceed to the right when Δ G < 0. b) The reaction can spontaneously proceed to the right when Δ G >0. c) The reaction is at equilibrium when Δ G = 0. d) All

12. An exothermic reaction which is spontaneous at all temperatures is a) C(graphite) + O2(g) CO2(g) ; Δ Ho =-393 kJ b) 3H2(g) + N2(g) 2NH3(g) ; Δ Ho=-46.2 kJ c) N2O4 (g) 2NO2(g) ; Δ Ho =+ 55.3 kJ d) All

13. A spontaneous reaction always occurs when : a) Δ Ho < 0 and Δ So < 0 b) Δ Ho > 0 and Δ So < 0 c) Δ Ho < 0 and Δ So > 0 d) Δ Ho > 0 and Δ So > 0

14. The equilibrium constant for a chemical reaction will be equal to one when a) Δ Ho < 0 and Δ So = 0 b) Δ Ho = 0 and Δ So =0 c) Δ Ho < 0 and Δ So > 0 d) Δ Ho > 0 and Δ So < 0

15. A change of state occurs within a system and produces 64.0kJ of heat. This heat is transferred to the surroundings at a constant pressure and a constant temperature of 300K. For this process, ΔS of the surrounding is :

a) 64.0 J/K b) -213.3 J/K c) 213.3 J/K d) 0.00 J/K

16. The volume of an ideal gas is doubled in an isothermal process. The change in entropy during this process is

a) -5.76JK-1 mol-1 b) +5.76 JK-1mol-1 c) +8.3 JK-1mol-1 d) 0 JK-1 mol-1

17. The efficiency of engine that is working between a lower temperature 27oC and a higher temperature 327oC is

a) 0.2 b) 0.35 c) 0.5 d) 1

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18. Ammonia gas a standard (Gibbs) free energy of formation equal to -16.367 kJ/mola) Find Δ Go for the reaction N2(g) + 3H2(g) <=> 2 NH3(g)

b) In which direction will this reaction proceed if a mixture of gases is made with : PNH3 = 1.00 atm PH2 = 0.50 atm PN2 = 0.50 atm

19. What is the change in entropy when 0.7 mol /l of CO2 and 0.3 mol /l of N2 each at one atm and 25o C blend to form a homogeneous mixture at the same conditions. Assume ideal gases.______________________________________________________1-a) Explain in detail the spontaneous process in terms of S, A and G- Prove

their values. b) Prove the combined equation of the first and the second law statement.

c) On heating, nitrosyl chloride NOCl at 650ºC, it decomposes into nitric oxide and chlorine:

2NOCl ↔ 2NO + Cl2

The reaction is endothermic, with H = 77.07 kJ/mol. If it may be assumed that both H and S are temperature invariant, and the standard molar entropies for NOCl, NO, and Cl2 are 261.2, 210.7 and 223.0 J/mol k, respectively. Calculate the equilibrium constant and the entropy of the universal.

2-a) Give different statements of the second law of thermodynamics. c) Find S for the process of transformation of 100 g water taken at 0º C into vapour at 120ºC. The heat of vaporization of water at 100º C is 2258.4 kJ / kg. The specific heat capacities of water at constant pressure for the liquid and gaseous states are 4.19 and 1.19 kJ /kg K respectively

3-a) Derive expression for the maximum thermodynamic efficiency of Carnot engine. b) Define the third law entropy and explain the term, reversible, in thermodynamics. c) One mole of an ideal gas at 27º C expands isothermally and reversibly from 10 to one bar against a pressure that is gradually reduced. Calculate q and W and each of the thermodynamic quantity U, H, G, A and S. 1- Prove the following: (b) Entropy of Mixing of ideal gases . (c) G = - RTlnK (d)fficiency of carnot cycle =1 - 1 / T2

(e) the combined equation of the first and the second law of thermodynamic. (f) the Clausius-Clapeyron equation.

2-(a) An ideal gas CP = 7R/2 is heated under constant volume from 70oC to 190oC, Calculate S. (b) What is the entropy of fusion of 1.00 mol of ice at 273.15 (heat of fusion is 6.008 kJ/mol) . (b) At what temperature will water boil at a space station where the atmospheric pressure is 490 mm Hg. The latent heat of vaporization of water is 545.5 cal g-1. The normal boiling point of water is 100o C . (c) The equilibrium constants for the following reaction at 1727oC and 2027oC are 4.08x 10-4 and 1.69 x 10-3 respectively. Calculate H for

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the reaction in kJ. N2(g) + O2(g) 2 NO(g). (d) An ideal heat engine is run between two temperatures of 550 K and 275 K. Calculate the Carnot efficiency for this heat engine.

2. a) Explain why G/T is more important than simply G in determining how Spontaneous process is? c) One mole of an ideal gas at 27º C expands isothermally and reversibly from 10 to one atm against a pressure that is gradually reduced Calculate q and W and each of the thermodynamic quantity U, H, G, A and S.

3. a) Prove the equations: ( i ) = o    + RT ln P / Po        .G o = RTlnKa         b)For certain reaction the equilibrium constants are 1.9 at 1000K and 6.5 at 900 K. calculate G and S at 1000K.

Mansoura University First term Examination Faculty of Science Subject: Chemistry (241) Chemistry Department Second level

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Course: Physical Chemistry Full Mark : 60 Marks Date ; January 2010 Time Allowed : 2hoursAnswer The Following Questions :

االجابة - 1 ورقة فى الصحيحة االجابة ورقة- 2 أكتب فى المسائل حل وضحورقتين االمتحان- 3 االجابة فى

I- Choose the response that best complete each statement: (2marks for each one)

1. The most correct statement below regarding the First Law of Thermodynamics is that:   a) A system can do work externally only if its internal energy decreases.  b)  The internal energy of a system that interacts with its environment must change. c) The only changes in the internal energy of a system are those produced by non- mechanical forces. d) The internal energy of a system cannot change if the heat transferred to the system is equal to the work done by the system.

2. For an isothermal expansion of an ideal gas, the change in enthalpy is: a) positive b) negative c) zero d) impossible to tell

2. During the adiabatic expansion of an ideal gas against atmospheric pressure, the internal energy will---------

a) increase b)decrease c) stay the same d) impossible to tell

4. The freezing of liquid water to form ice a) results in uptake of heat from the surroundings b) results in release of heat to the surroundings c) results in no transfer of heat to or from the surroundings d) whether heat is taken up or given off during freezing depends on the temperature

3. Which of the following statements is FALSE? (H, G, and S refer to system

changes.) a) S must be positive for a process to be spontaneous. b) G is always positive for nonspontaneous processes. c) If S is negative then H must be negative for a spontaneous process. d) G is always negative for spontaneous processes.

4. The heat capacity at constant volume is ________ the heat capacity at constant pressure for an ideal gas. a) greater than b) less than c) the same as d)cannot determine

5. An ideal gas is compressed isothermally and reversibly from two liters to one liter, then expanded adiabatically and reversibly back to 2 liters. The overall change in temperature of the gas is--------

a) positive b) negative c) zero d) impossible to tell

8. For free expansion of an ideal gas A) W = Δ U = q = 1 b) W≠ Δ U ≠ q

c) W = Δ U = q = 0 d) none of these answers

9. For isothermal irreversible expansion of an ideal gas the work done is given by .

a) W = nRT ln P1/P2 b) W = - U

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c)W = nRT ( 1-P2/P1) d) none of these answers

10. For which of the following compounds is it thermodynamically not feasible to synthesize the compound from the elements under standard conditions :(ΔGf° of NH3, NO and N2O are - 16.5, + 86.6 and + 104.2 kJmol-1 respectively. a) NO only b) N2O and NO c) N2O only d) NH3 and N2O

II- Answer The Following Questions ( 2 marks for each one ) 1. Place the following compounds in order of increasing S°: PCl5(s), PCl5(g) and PCl3(g).

a) PCl5(s) < PCl5(g) < PCl3(g) b) PCl5(s) < PCl3(g) < PCl5(g) c) PCl5(g) < PCl5(s) < PCl3(g) d) PCl5(g) < PCl3(g) < PCl5(s)

2. Fill in the blanks: If ) ΔG°<0, then K is ______. If ) ΔG°>0, then K is ______. If ) ΔG°=0, then K is ______.The answers in order are

a) >1, < 1, =1 b) < 1, >1, =1 c) < 0, > 0, = 0 d) > 0, < 0, = 0

3. N2(g) + 3 H2(g) ---> 2 NH3(g) The reaction indicated above is thermodynamically spontaneous at 298 K, but becomes nonspontaneous at higher temperatures. Which of the following is true at 298 K?

a) ∆G, ∆H, and ∆S are all positive. b) ∆G, ∆H, and ∆S are all negative.c) ∆G and ∆H are negative, but ∆S is positive. d) ∆G and ∆S are negative, but ∆H is positive.

4. The entropy of the universe----------------------------- a) is zero. b) remains constant. c) is always increasing. d) is also decreasing.

5. Which process is accompanied by a decrease in entropy of the materials? a) expansion of a gas into a vacuum b) solution formationc) freezing of a liquid d) thermal equalization between two regions in thermal contact

6. Which of the following reactions would have a positive slope if Go for the reaction were plotted as a Function of temperature? a) PCl3(g) + Cl2(g) PCl3(g) b) 2KClO3(s) 2 KCl(s) + 3O2(g)

c) CO(g) + H2O(g) CO2(g) + H2(g) e) C5H12(l) + 8 O2(g) 5 CO2(g) + 6 H2O(g

7. Identify the INCORRECT statement below: a) An endothermic process which is spontaneous must have a positive S. b) Every naturally occurring spontaneous process is attended with an increase in the entropy of the universe.c) The Gibb's free energy of the system always increases in a spontaneous process.d) A process which causes the system entropy to decrease can still be

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spontaneous if an even larger entropy increase takes place in the surroundings.

8. Identify the INCORRECT statement below: a) In spontaneous changes the universe tends toward a state of greater disorder. b) The Gibbs free energy of a system is increasing in any spontaneous process going on at constant T and P. c) The entropy of a pure, perfect crystal at T = 0 K is zero. d) The entropy of a system can decrease in a spontaneous process, if the surrounding entropy is increasing even more.

9. The free energy of mixing of two immiscible liquids is : a) positive b) negative c) zero d) cannot tell

10. The equilibrium constant for a chemical reaction will be equal to one (1) under which one of the following conditions? a) Ho < 0 and So = 0 b) Ho = 0 and So = 0 c) Ho < 0 and So > 0 d) Ho > 0 and So < 0

III. Answer The Following Questions ( 4 marks for each one )

1. Starting with the equation q = ΔU + W, show that using the ideal gas equation and the relation, Cp - Cv = R and If a gas expands adiabatically and reversibly the relation between V and P can be expressed as

2. One mole of ideal gas at 27 ˚C and 100 bar is allowed to expand reversibly and isothermally to 5 bar. Calculate the amount of heat adsorbed._____________________________________________________________________IV. Answer The Following Questions ( 4 marks for each one )

1. At what temperature will water boil at a space station where the atmospheric pressure is 490 mm Hg. The latent heat of vaporization of water is 545.5 cal g-1.The normal boiling point of water is 100o C .

2. An ideal heat engine is run between two temperatures of 550 K and 275 K. Calculate the Carnot efficiency for this heat engine.

3. Derive expression for ΔSmix.

GOOD LUCK,

Mansoura University Second term ExaminationFaculty of Science Subject : Chemistry (2) Chemistry Department Second Year Course: Physical Chemistry Full Mark : 70 Marks Date ; Sunday , 8 June 2008 Time Allowed : 3 hoursSECTION A: Chemical thermodynamic, 35 marks.

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االجابة -1 ورقة فى الصحيحة االجابة ورقة- 2 أكتب فى المسائل حل وضح ين ورقت فى االمتحان- 3 االجابة

I. Choose the response that best completes each statement. ( one mark for each one ) 1. The second law of thermodynamics states that:

a) The entropy of a perfect crystal is zero at 0 K. b) The entropy of the universe is constant in any naturally occurring process.c) The energy of the universe is increasing in any naturally occurring process.d) The entropy of the universe is increasing in any naturally occurring process..

2. There are two properties of a reacting system that determine whether a process at constant pressure and temperature can occur spontaneously. These are:

a) Kinetic and potential energy changeb) Heat and workc) Energy change and enthalpy changed) Enthalpy change and entropy change

3. Which of the following statements is FALSE? (H, G, and S refer to system changes.) a) S must be positive for a process to be spontaneous.b) G is always positive for nonspontaneous processes.c) If S is negative then H must be negative for a spontaneous process.d) G is always negative for spontaneous processes.

4. Identify the INCORRECT statement below: a) Energy is the capacity to do work or transfer heat. b) According to the First Law of Thermodynamics, the total amount of energy in the universe is constant. c) Endothermic processes require the absorption of energy to occur, corresponding to a positive H. d) The Gibbs free energy G of a system is increasing in any spontaneous process.

5. For which of the following compounds is it thermodynamically not feasible to synthesize the compound from the elements under standard conditions :(ΔfG° of NH3, NO and N2O are - 16.5, + 86.6 and + 104.2 kJmol-1 respectively. a) NO only b) N2O and NO c) N2O only d) NH3 and N2O

6. Which of the following reactions would have a positive slope if Go for the reaction were plotted as a Function of temperature?

a) PCl3(g) + Cl2(g) PCl3(g) b) 2KClO3(s) 2 KCl(s) + 3O2(g)

c) CO(g) + H2O(g) CO2(g) + H2(g) e) C5H12(l) + 8 O2(g) 5 CO2(g) + 6 H2O(g)

7. Consider the reaction A(g) B(g). Assuming ideal gas behavior, under what conditions rG0 = rG?a) PB >> PA b) QP = KP c) QP < 0 d) PB = PA

8. The quantity TS may be expressed in units of a) J b) K c) J K d) J K-1

9. The free energy of mixing of two immiscible liquids is : a) positive b) negative c) zero d) cannot tell

10. The entropy will usually decrease when 1) A solid changes to a liquid

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2) A chemical reaction occurs that results in a decrease in the number of moles of gas. 3) A liquid changes to gas. 4) A molecule is formed from two or more atoms

a) 1 and 2 only b) 2, 4 only c) 1, 2 ,3 and 4 d) 1 and 3 II. Answer the following questions 1. For the following reactions, predict and explain whether they will tend to be spontaneous at either high or low temperatures, or at all temperatures, or nonspontaneou at all temperatures. (2 marks for each one) a) H2(g) + 1/2O2(g) H2O(l) H = -286 kJ b) H2(g) + Cl2(g) 2HCl(g) H = -185 kJ c) HCO2H(l) HCO2H(g) H = 46.60 kJ kJ

2. The equilibrium constant for the formation of phosgene is measured at two different temperatures.CO(g) + Cl2(g) COCl2(g) a) At 506oC, Keq = 1.3, and at 350oC, Keq = 0.78. Calculate S for this reaction at 350oC .

(4 marks)

3. Write on the following: (3 marks for each one) a) The third law of thermodynamic. b) Combined first and second laws of

thermodynamic.

4. We mix together 36.3 g of silicon and 14.1 g of germanium and melt it, then cool it into a solid solution at 25oC. Assume both the liquid and solid solutions are ideal. What are the molar entropy and molar free energy of mixing at 25oC? (Ge = 72.6 g/mol , Si = 28.2 g/mol). (3 marks)

5. Calculate the change in entropy of the system, S, and the change in entropy of the surroundings, Ssurr, when one mole of an ideal gas is expanded isothermally and reversibly from a pressure of 5.0 bar to 1.0 bar at 300 K. What is the entropy of the universe? (4 marks)

6. What is the maximum efficiency of an ideal heat engine for which the temperature of the cold reservoir is 250 K and the temperature of the hot reservoir is 500K? (2 marks)

Mansoura UniversityFaculty of ScienceChemistry DepartmentFinal Examination in Physical and Inorganic Chemistry for Second year Students. June, 2006 Time: 3hrs

I. Choose the best answer ( You must support your answer for credit )

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1. Predict whether the entropy change for the following reactions is positive, negative, or approximately zero. 

i. MgCO3 (s) MgO (s) + CO2 (g)  ii. Zn (s) + 2HCl (aq) ZnCl2 (aq) + H2 (g)  iii. H2 (g) + CO2 (g) H2O (g) + CO (g)  iv. 2Pb (s) + 3 O2 (g) 2PbO (s) + 2SO2 (g)

a- + - ++ b. + ~ 0 - + c. - + - ~ 0 d. + + ~ 0 - 2. According to the second law of thermodynamics, a process will be spontaneous if it results in:

a. A decrease in the internal energy of the system.  b. An increase in the entropy of the universe.  c. An increase in the free energy of the system.  d. decrease in the entropy of the surroundings. 

3. For a particular chemical reaction, Ho is positive and So is negative. Which of the following statements about the spontaneity of the reaction under standard conditions is TRUE?

a. The reaction will be spontaneous only if the magnitude of Ho is large enough to overcome the unfavorable entropy change. b. The reaction will be spontaneous only if the magnitude of So is large enough to overcome the unfavorable enthalpy change. c. The reaction will be spontaneous regardless of the magnitudes of Ho and So. d. The reaction cannot be spontaneous.

4. Fill in the blanks:The Three Laws of Thermodynamics, not necessarily in order, are:The total --------- of the universe increases for a spontaneous process.The total ----------of the universe is constant.The --------- of a perfectly ordered crystal at 0 K is 0.The answers in order (top to bottom) are

a. energy, entropy, entropy b. entropy, energy, entropy c. energy, entropy, energy e. energy, energy, energy

5. Place the following compounds in order of increasing S°: PCl5(s) PCl5(g) PCl3(g)

(a) PCl5(s) < PCl5(g) < PCl3(g) (b) PCl5(s) < PCl3(g) < PCl5(g)(c) PCl5(g) < PCl5(s) < PCl3(g) (d) PCl5(g) < PCl3(g) < PCl5(s)

6. Which of the following is NOT a state function? a.G b. W c. H d. S

7. The condensation of any gas to a liquid is expected to have a. a positive ΔH and a positive ΔS b. a positive ΔH and a negative ΔS c. a negative ΔH and a negative ΔS d. a negative ΔH and a positive ΔS

8. The third law of thermodynamics states that: a. the entropy of the universe is increasing.

b. the entropy of the universe is constant. c. the entropy is zero at 0 K for a perfect crystal.

d. the absolute entropy of a substance decreases with increasing temperature.

9. Which of the following reactions is unfavorable at low temperatures but becomes favorable as the temperature increases?

a. 2 CO(g) + O2(g) --> CO2(g); Ho = -566 kJ; So = -173 J/K b. 2 H2O(g) --> 2 H2(g) + O2(g); Ho = 484 kJ; So = 90.0 J/K c. 2 N2O(g) --> 2 N2(g) + O2(g); Ho = -164 kJ; So = 149 J/K d. PbCl2(s) --> Pb2+(aq) + O2(g); Ho = 23.4 kJ; So = -12.5 J/K

10. Fill in the blanks:

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If ) ΔG°<0, then K is __. If ) ΔG°>0, then K is __. If ) ΔG°=0, then K is ___.The answers in order are

a. >1, < 1, =1 b. < 1, >1, =1 c. < 0, > 0, = 0 d. > 0, < 0, = 0 II. Answer Five of the following:

1. What is the maximum efficiency of an ideal heat engine for which the temperature of the cold reservoir is 250 K and the temperature of the hot reservoir is 350 K higher? 2. The Haber reaction has the following thermodynamic property: N2(g) + 3H2(g) 2NH3(g) H0

298 = -92.2 kJ/mol If the value of Keq at 298K = 1.01, what will be the value of Keq at 500°C? 3. Calculate G° in kJ/mol for the combustion of methane: 

CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (g) The following are G0

f in kJ/mol: CH4 = -50.8,   CO2 = -394.4,   H2O = -237.2.4. Calculate the entropy change for 1.00 mole of HF when it is cooled at constant pressure from 500 K to 298.15 K. Cp = (5/2)R.5. Determine the normal boiling point of Mercury, Hg, in K, from the following data assuming that H° and S° are independent of temperature.

Substance H0f(kJ.mol-1) S° (J mol-1 K-1)

Hg (liquid) 0 77.4Hg (gas) 60.8 174.7

6. Prove that = o    + RT ln P / Po    

14. For adiabatic expansion of an ideal gas the relation between volume and pressure is given by

A) V/T = constant B) VT = constant C) PV g = constant D) [T/V] g-1 = constant

15. For isothrmal expansion of an ideal gas A) q = U B) q = U +W C) q = W D. q = U

16. For isothermal irreversible expansion of an ideal gas the work done is given by . A) W = nRT ln P1/P2 B) W = - U C) W = nRT ( 1-P2/P1) D) none of these answers

17.When there is no exchange of heat between the system and surroundings the process is said to be A) Isothermal B) Isobaric C) Adiabatic D) Isochoric

18.For free expansion of an ideal gasA) W = Δ U = q = 1 B) W≠ Δ U ≠ q C) W = Δ U = q = 0 D) none of these answers

19. Prove for ideal gas expands adiabatically T2 = T1 (V1/V2) ] g-1

20. One mole of ideal gas at 27 ˚C and 100 bar is allowed to expand reversibly and isothermally to 5 bar. Calculate the amount of heat adsorbed

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