ThermoDynamics
Name (last)________________(First)______________________
Practice Exam Thermodynamics
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 gal = 4 qt
1 lb = 16 oz
T  F = 1.8T  C + 32
1 mile = 5280 ft
1 qt = 57.75 in3
1 ton = 2000 lb
1 yd = 3 ft
SI-
1 in = 2.54 cm
1 L = 1.057 qt
1 lb = 453.6 g
English:
1 mi = 1.609 km
1 qt = 0.946 L
1 oz = 28.35 g
Misc. info
1 mole = 6.02•1023
Thermodynamics
T C =
Thermodynamics
ΔG = ΔH - TΔS
State Function (X) where X = E, H, S or G
ΔG = ΔG° + RT ln Q
w = -P
ΔV
ΔE = q + w
ΔG° = - RT ln Keq
Keq = exp {-ΔG° /RT}
ln Keq = (ΔS°/ R) - (ΔH°/ RT)
ΔH = ΔE + P ΔV
ΔH = qp = m Cs ΔT
ΔS°univ = ΔS°surr + ΔS°sys
ΔS°surr = - ΔH°sys / T
1.8
R = 8.314 J/ mol•K or .08206 L•atm/mol•K
Universe = surroundings + system
ΔXrxn = Σn ΔX°prod - Σn ΔX°react
(T  F − 32)
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
c) Third Law of Thermodynamics
3
b) Second Law of T Thermodynamics
d) This statement violates all Laws of Thermodynamics
If the heat of reaction is endothermic, which of the following is always true?
a) the reaction is fast
c) the reaction is slow
4
b) the energy of the reactants is greater than the products
d) the energy of the reactants is lower than the products
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
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
ΔH = 2(-46.19) - [0 + 0] = - 92.38 kJ
ΔG = 2(-16.66) - [0 + 0] = - 33.32 kJ
ΔS = 2(192.5) - [191.50 + 3(130.580)] = - 198.24 J
8
d) Avogadro
d) 348 K
T =
ΔH
ΔS
=
92380
198.24
= 466 K
€
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
12
13
ii
+
0
-
Spontaneous
iii
-
+
+
Not Spontaneous
iv
0
-
-
Spontaneous
v
-
0
+
non-spontaneous
vi
+
+
-
TΔS > ΔH
non-spontaneous
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
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
iii) Which of the following is not a state function?
a) work
b) q (constant pressure)
c) Entropy
d) outlaw
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.
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)
326.8 kJ/mol
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.