ThermoDynamics

Practice Exam Thermodynamics Name (last)________________(First)______________________

Read all questions before you start. Show all work and explain your answers to receive full credit. Report all numerical answers to the proper number of significant figures. By signing your signature above you agree that you have worked alone and neither give nor received help from any source. Keep your eyes on your own paper at all times

System LENGTH: VOLUME MASS Temperature

English: 1 ft = 12 in

1 mile = 5280 ft

1 yd = 3 ft

1 gal = 4 qt

1 qt = 57.75 in3

1 lb = 16 oz

1 ton = 2000 lb

T F = 1.8T C + 32

SI-

English:

1 in = 2.54 cm

1 mi = 1.609 km

1 L = 1.057 qt

1 qt = 0.946 L

1 lb = 453.6 g

1 oz = 28.35 g T C =

(TF−32)1.8

Misc. info 1 mole = 6.02•1023 R = 8.314 J/ mol•K or .08206 L•atm/mol•K

Thermodynamics

Universe = surroundings + system

State Function (X) where X = E, H, S or G

ΔXrxn = Σn ΔX°prod - Σn ΔX°react

w = -P ΔV

ΔE = q + w

ΔH = ΔE + P ΔV

ΔH = qp = m Cs ΔT

ΔS°univ = ΔS°surr + ΔS°sys

ΔS°surr = - ΔH°sys / T

Thermodynamics

ΔG = ΔH - TΔS

ΔG = ΔG° + RT ln Q

ΔG° = - RT ln Keq

Keq = exp {-ΔG° /RT}

ln Keq = (ΔS°/ R) - (ΔH°/ RT)

Temperature Conversion

°C = 5/9 ( __°F - 32)

°F = ( 9/5 _°C ) + 32)

Multiple -choice. Show work for partial credit. 1 Consider the room temperature condensation of steam: H2O (g) H2O (l). Which parameter is positive?

a) ΔH b) ΔS c) ΔG d) none 2 Which law of thermodynamics states that energy in, equals energy out: Energyin = Energyout.

a) First Law of Thermodynamics b) Second Law of T Thermodynamics c) Third Law of Thermodynamics d) This statement violates all Laws of Thermodynamics

3 If the heat of reaction is endothermic, which of the following is always true?

a) the reaction is fast b) the energy of the reactants is greater than the products c) the reaction is slow d) the energy of the reactants is lower than the products

4 Which among the following has the lowest entropy?

a) H2O(g) b) H2O(l) c) H2(l) d) All the same

5 Which gas law states that at zero Kelvin, matter ceases to have volume?

a) Boyle b) Gay-Lussac c) Charles d) Avogadro

6 What will happen to a reaction if Hsys < 0 and Ssys < 0 ?

a) will never proceed spontaneously to the right. b) proceed spontaneously to the right only at low temperatures. c) proceed spontaneously to the right only at high temperatures. d) proceed spontaneously to the right at all temperatures.

7 Consider the formation of ammonia: N2(g) + 3 H2(g) 2 NH3(g) Assuming that H° and S° are constant with temperature, find

the temperature at which Kp = 1.00.

a) 695 K b) 233 K c) 466 K d) 348 K

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ΔH = 2(-46.19) - [0 + 0] = - 92.38 kJΔG = 2(-16.66) - [0 + 0] = - 33.32 kJΔS = 2(192.5) - [191.50 + 3(130.580)] = -198.24 J

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T = ΔHΔS

= 92380198.24

= 466 K

8 When water freezes at 0°C, which of the following is always true?

a) Keq = 0 b) ΔG = 0 c) Q = 0 e) ΔS = 0

9 Which thermodynamic parameter is equal to the difference between the energy of the product and the energy of the reactant at

constant pressure? a) ΔG Sys b) E cell c) ΔS sys d) ΔH sys

10 The super zero, ( ° ) in the state functions S°, E°, H° and G° stands for:

a) Standard state. b) raising the state function to the zeroth power. c) Temperature at absolute zero. d) an oxidation state of zero for the system.

11 Supply the missing information (question marks) in each row of the following table: ΔSrnx ΔHrxn ΔGrxn Comment

i + - - Spontaneous

ii + 0 - Spontaneous

iii - + + Not Spontaneous

iv 0 - - Spontaneous

v - 0 + non-spontaneous

vi + + - TΔS > ΔH

non-spontaneous

12 For each of the following group, arrange each system in order of increasing standard entropy, S°, and explain your choice. ( lowest (1) – medium (2) - highest (3) )

i) K, Li, Rb: Li (1) < K (2) < Rb (3) Complexity, atomic mass

ii) HF, HBr, HCl: HF (1) < HCl (2) < HBr (3) Complexity, Molar mass

iii) hot water, steam, ice water: Ice water (1) < Hot water (2) < Steam (3) Phase and Temperature

iv) diamond, charcoal, graphite: graphite (1) < diamond (2) < charcoal (3) Complexity, organization of carbon 13 i) The Entropy in the universe is always

a) increasing b) decreasing c) zero d) constant ii) Which law of thermodynamics states the condition of spilled water.

a) first law b) second law c) third law d) outlaw iii) Which of the following is not a state function?

a) work b) q (constant pressure) c) Entropy d) Free Energy

14 You must follow the directions for this question. Arrange each of the following groups in order of increasing state function, X°, and explain your choice. The order

should be smallest or most negative (1) to medium (2) to largest or most positive (3). Place numerical value for each choice, 1, 2 or 3 after placing them in order and justify your answer.

i) Enthalpy: (a) 2.0 gram of NH3 (g), (b) 1.0 gram of CH4 (g), (c) 2.0 grams of HCl(g)

ii) Entropy: (a) Na(s) + C(s) + 3/2 O2(g) , (b) NaCO3(s) , (c) NaO(s) + CO2(g)

iii) Free energy under standard conditions: (a) Cr+3/Cr, (b) Ag+/Ag, (c) Ga+3/Ga

15 The excessive production of ozone (O3) gas in the lower atmosphere causes rubber to deteriorate, green plants to turn brown, and

persons with respiratory disease to have difficulty breathing. i) Is the formation of O3 from O2 favor at all temperature, at no temperature, at high temperature, or low temperature ? ii) Calculate ΔG° for this reaction at 298 K and 1 atm. 326.8 kJ/mol

iii) Calculate ΔG, at 298 K for this reaction urban smog where [O2] = 0.21 M and [O3] = 5•10-7 M The reaction is: 3 O2 (g) 2 O3 (g)

16 Check mark if you agree or disagree with the following statement, then write a short convincing explanation to support or refute

the statement. No credit will be given without justification. i) __ Agree __ Disagree: All reactions with equilibrium constant greater than one (Keq > 1) are spontaneous.

ΔG = -RT lnKeq for Keq >1, ΔG becomes negative. ii) __ Agree __ Disagree: All spontaneous reactions occur quickly.

Kinetics and Thermodynamics occur independently from each other.

iii) __ Agree __ Disagree: The electrolysis of salt water will result in the oxidation of Na+ at the anode. The oxidation and reduction of water occurs at a lower potential of ~ 2.1 V

iv) __ Agree __ Disagree: The following line-notation represents a voltaic cell. Ag(s)|Ag+(aq) || Cd+2(aq) | Cd(s)

v) _+_ Agree __ Disagree: A typical car batter can carry a voltage greater than 12 Volts .

If the concentration of reactant is higher than 1M, then the Nernst equation will show a potential of greater than 12 V for a car battery.

vi) __ Agree _+_ Disagree: Positive electromotive force corresponds to positive free energy and positive ΔS(Universe).

False, positive EMF, according to ΔG = - nFE, yields a negative free energy (and postive ΔSUniverse).

17 Kw at 25° = 1.01 •10-14, and Kw at 50° = 5.48•10-14. What is ΔH, ΔS and ΔG for the auto-ionization of water at 25°?

ΔG° = 79.8 kJ/mol, ΔH° = 55.8 kJ/mol, ΔS = -80.6 J/mol 18 In photosynthesis, CO2 (g) and H2O(g) is converted to glucose C6H12O6 (s) and oxygen (O2) (g). at 298 K.

6 CO2 (g) + 6 H2O(g) C6H12O6 (s) + 6 O2 (g) [C6H12O6 (s) : ΔHf° = -1268.0 KJ/mol, ΔSf° = -212.0 J/mol•K ]

a) Is this an exothermic or endothermic process? Calculated ΔH° rxn. b) What is ΔS sys, ΔS surr ? c) Calculate Keq for this reaction.

19 Consider the formation of methyl alcohol from carbon monoxide and hydrogen: 2 CO (g) + 4 H2 (g) 2 CH3OH (g)

a) What are ΔH° and ΔS° for the reaction (T= 298 K)? In what direction will this reaction proceed spontaneously? b) Calculate ΔG°rxn (T = 298 K and P = 1 atm for all species) c) At what temperature will the spontaneity of the reaction reverse itself ?

20 During a hot summer day, your friend suggests opening the door of your refrigerator to cool your kitchen. Will his strategy work?

Discuss your answer in terms of thermodynamics.

21 During a hot summer day, your friend suggests opening the door of your refrigerator to cool your kitchen. Will his strategy work?

Discuss your answer in terms of thermodynamics.