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Unformatted text preview: Practice problems fall 2011
Name___________________________________ R.Lopez de la Vega
Bubble in the form number in the section entitled Grade or Educ in the scantron.
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) Which of the following is a nonspontaneous process?
A) the expansion of a gas into a vacuum
B) 2 NH3 (g) → N2 (g) + 3 H2 (g) if PNH₃ = 1 atm, PH₂ = PN₂ = 0, and Kp = 2 × 10-6
C) N2 (g) + 3 H2 (g) → 2 NH3 (g) if PH₂ = PN₂ = 1 atm, PNH₃ = 0, and Kp = 4 × 105 1) D) none of the above
2) Which of the following processes is spontaneous?
A) precipitation of solute from a saturated solution
B) reaction of sodium with oxygen
C) water flowing uphill
D) a mixture of two gases separating into pure compounds 2) 3) Classify each of the following processes as spontaneous or nonspontaneous.
I. H2O(l) → H2O(g) T = 25°C vessel open to atmosphere with 50% relative
II. H2O(s) → H2O(l) T = 25°C P = 1 atm
A) I and II are both nonspontaneous.
B) I and II are both spontaneous.
C) I is nonspontaneous and II is spontaneous.
D) I is spontaneous and II is nonspontaneous. 3) 4) Which provides the greatest increase in entropy?
A) H2O (g, 0.1°C) → H2O (s, 0.1°C)
C) H2O (l, 0°C) → H2O (l, 25°C) 4)
B) H2O (s, 0°C) → H2O (l, 0°C)
D) H2O (l, 100°C) → H2O (g, 100°C) 5) For a spontaneous process
A) energy and entropy are conserved.
B) the energy of the system and the surroundings decreases and the entropy of the system
and surroundings increases.
C) energy is conserved and the entropy of the system and surroundings increases.
D) both the energy and the entropy of the system and surroundings decrease. 5) 6) For a particular process ΔG is less than ΔH. Therefore
A) ΔS is zero.
B) ΔS is negative.
C) ΔS is positive.
D) ΔS is negative if ΔH is positive and ΔS is positive if ΔH is negative. 6) 1 7) The brown color associated with photochemical smog is due to NO2(g), which is involved in
an equilibrium with N2O4(g) in the atomosphere.
2 NO2(g) ⇌ N2O4(g)
Predict the signs of the enthalpy and entropy change for this reaction.
A) The enthalpy change is negative and the entropy change is positive.
B) The enthalpy change is positive and the entropy change is negative.
C) The enthalpy change is positive and the entropy change is positive.
D) The enthalpy change is negative and the entropy change is negative. 7) 8) The signs of ΔG, ΔH, and ΔS at 25°C are shown below for three reactions. 8) reaction ΔG ΔH ΔS
Which reaction could go in the reverse direction at high temperature?
B) I and II
C) I D) III
9) 9) Which of the following is zero at 25°C?
A) ΔG°f for N2(g) B) ΔG°f for H2O (l) C) S° for H2O (l) D) S° for N2 (g) 10) Predict the sign of ΔS for both of the following processes.
I. 2 C(graphite) + O2(g) → 2 CO(g)
II. C4H10(g) → C4H10(l)
A) ΔS should be positive for I and negative for II.
B) ΔS should be negative for I and positive for II.
C) ΔS should be negative for I and negative for II.
D) ΔS should be positive for I and positive for II. 10) 11) If ΔG° is negative for a reaction,
A) K < 0.
C) K is between 0 and 1. 11)
B) K > 1.
D) K = 0. 12) Calculate the standard free energy for the reaction given.
2 CH3OH(l) + 3 O 2(g) → 2 CO 2(g) + 4 H2O(l) Species ΔG°f kJ/mol CH3OH ( l) -166.3 O2 (g)
CO 2 (g) 0.00
-394.4 H2O (l) 12) -237.1 A) -465.2 kJ B) -1404.6 kJ C) -797.8 kJ 2 D) -2069.8 kJ 13) The standard molar entropy for Br2(g) is 245.46 J/(mol · K) at 25°C. Given that ΔS° = 104.58 J/K
for the dissociation of one mole of Br 2(g) into Br(g) at 25°C, find the standard molar entropy
for Br(g) at 25°C.
A) 70.44 J/(mol · K)
B) 140.08 J/(mol · K)
C) 350.04 J/(mol · K)
D) 175.02 J/(mol · K) 13) 14) Which substance will have the highest standard molar entropy at 25°C ?
C) MgCO3(s) 14)
D) C(graphite) 15) Under which of the following conditions would one mole of Ne have the highest entropy, S?
A) 137°C and 35 L
B) 27°C and 25 L
C) 27°C and 35 L
D) 137°C and 25 L 15) 16) The figure represents the spontaneous evaporation of nitrogen in which liquid nitrogen, N2(l), 16) becomes gaseous nitrogen, N2(g): N2(l) → N2(g). What are the signs ( + or -) of ΔH, ΔS, and
ΔG for this process? A) ΔH = +, ΔS = +, ΔG = C) ΔH = -, ΔS = -, ΔG = - B) ΔH = +, ΔS = +, ΔG = +
D) ΔH = -, ΔS = -, ΔG = + 17) Calculate ΔS° for the formation of one mole of solid sodium bromide from the elements at
25°C. 17) Species S°, J/(K · mol)
A) 86.8 J/K B) -116.7 J/K C) -81.2 J/K D) -40.6 J/K 18) Which of the three laws of thermodynamics provides a criterion for spontaneity?
A) the second law of thermodynamics
B) the first law of thermodynamics
C) the third law of thermodynamics
D) both the second and third laws of thermodynamics 18) 19) Which of the following is a criterion for spontaneity that holds for any process?
A) ΔG > 0
B) ΔG < 0
C) ΔStotal > 0
D) ΔStotal < 0 19) 20) For the reaction 3 C2H2(g) → C6H6(l) at 25°C, the standard enthalpy change is -631 kJ and the
standard entropy change is -430 J/K. Calculate the standard free energy change at 25°C.
A) -1061 kJ
B) -618 kJ
C) 948 kJ
D) -503 kJ 20) 3 21) The solubility of manganese(II) fluoride in water is 6.6 g/mL at 40°C and 4.8 g/L at 100°C.
Based on these data, what is the sign of ΔH° and ΔS° for the process below?
MnF 2(s) ⇌ Mn2+(aq) + 2 F -(aq)
A) ΔH° is negative and ΔS° is positive.
B) ΔH° is positive and ΔS° is positive.
C) ΔH° is negative and ΔS° is negative.
D) ΔH° is positive and ΔS° is negative. 21) 22) For bromine, ΔH°vap = 30.91 kJ/mol and ΔS°vap = 93.23 JK-1mol-1 at 25°C. What is the
normal boiling point for bromine?
D) 332°C 22) 23) Which statement is true about the formation of CaCO3(s) from CaO( s) and CO 2(g) at 1.00
CaO(s) + CO2(g) → CaCO3(s) ΔH° = -178.7 kJ and ΔS° = -150.4 J/K
A) The reaction is not spontaneous at any temperature.
B) The reaction is spontaneous at high temperatures.
C) The reaction is spontaneous at all temperatures.
D) The reaction is spontaneous at low temperatures. 23) 24) Consider the reaction:
N2(g) + 3 F 2(g) → 2 NF3(g) ΔH° = -249 kJ and ΔS° = -278 J/K at 25°C
Calculate ΔG° and state whether the equilibrium composition should favor reactants or
products at standard conditions.
A) ΔG° = -332 kJ; the equilibrium composition should favor reactants.
B) ΔG° = -166 kJ; the equilibrium composition should favor reactants.
C) ΔG° = -166 kJ; the equilibrium composition should favor products.
D) G° = -332 kJ; the equilibrium composition should favor products. 24) 25) In general, as a reaction goes to equilibrium
A) ΔG decreases. 25)
B) ΔG° decreases. C) ΔG goes to zero. D) ΔG°f decreases. 26) ΔG = ΔG° for a reaction
A) at the start of the reaction.
C) if Q = 1. 26)
B) if Q = K.
D) at STP. 4 Answer Key
Testname: PRACTICE17 1) D
26) C 5 ...
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- Fall '08