35
105) What are the signs of ΔH and ΔS for the reaction represented in the above drawing?
A) ΔH = +, ΔS = +
B) ΔH = +, ΔS = –
C) ΔH = –, ΔS = +
D) ΔH = –, ΔS = –
106) The reaction represented in the above drawing is likely to be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and non spontaneous at high temperatures.
D) spontaneous at all temperatures.
The following drawing is a representation of the exothermic reaction in which ozone forms
dioxygen.
107) What are the signs of ΔH and ΔS for this reaction?
A) ΔH = +, ΔS = +
B) ΔH = +, ΔS = –
C) ΔH = –, ΔS = +
D) ΔH = –, ΔS = –
108) This reaction is likely to be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and nonspontaneous at high temperatures.
D) spontaneous at all temperatures.
109) The following drawing is a representation of a reaction of the type A → B, where different
shaded spheres represent different molecular structures. For this reaction ΔH° = +45 kJ. This
reaction is likely to be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and nonspontaneous at high temperatures.
D) spontaneous at all temperatures.
110) The following drawing is a representation of a reaction of the type A → B, where different
shaded spheres represent different molecular structures. For this reaction ΔH° = -30 kJ. This
reaction is likely to be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and nonspontaneous at high temperatures.
D) spontaneous at all temperatures.
111) The following drawing is a representation of a reaction for which ΔH° = +62 kJ. This
reaction is likely to be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and nonspontaneous at high temperatures.
D) spontaneous at all temperatures.
112) The following drawing is a representation of a reaction for which ΔH° = -22 kJ. This
reaction is likely to be
A) nonspontaneous at all temperatures.
B) nonspontaneous at low temperatures and spontaneous at high temperatures.
C) spontaneous at low temperatures and nonspontaneous at high temperatures.
D) spontaneous at all temperatures.
8.2 Algorithmic Questions
1) For a process at constant pressure, 49,600 calories of heat are released. This quantity of heat is
equivalent to
A) 4.82 × 10-6 J.
B) 1.19 × 104 J.
C) 1.24 × 104 J.
D) 2.08 × 105 J.
2) Calculate the work, w, gained or lost by the system when a gas expands from 15 L to 40 L
against a constant external pressure of 1.5 atm. 1 L ∙ atm = 101 J.
A) -6.1 kJ
B) -3.8 kJ
C) +3.8 kJ
D) +6.1 kJ
3) For a particular process that is carried out at constant pressure, q = 145 kJ and w = -35 kJ.
Therefore,
A) ΔE = 110 kJ and ΔH = 145 kJ.
B) ΔE = 145 kJ and ΔH = 110 kJ.
C) ΔE = 145 kJ and ΔH = 180 kJ.
D) ΔE = 180 kJ and ΔH = 145 kJ.
4) When 5.00 mol of benzene is vaporized at a constant pressure of 1.00 atm and at its normal
boiling point of 80.1°C, 169.5 kJ are absorbed and PΔV for the vaporization process is equal to
14.5 kJ then
A) ΔE = 155.0 kJ and ΔH = 169.5 kJ.
B) ΔE = 184.0 kJ and ΔH = 169.5 kJ.
C) ΔE = 169.5 kJ and ΔH = 184.0 kJ.
D) ΔE = 169.5 kJ and ΔH = 155.0 kJ.
5) When 10.00 moles of H2(g) reacts with 5.000 mol of O2(g) to form 10.00 mol of H2O(l) at
25°C and a constant pressure of 1.00 atm. If 683.0 kJ of heat are released during this reaction,
and PΔV is equal to -37.00 kJ, then
A) ΔH° = +683.0 kJ and ΔE° = +720.0 kJ.
B) ΔH° = +683.0 kJ and ΔE° = +646.0 kJ.
C) ΔH° = –683.0 kJ and ΔE° = -646.0 kJ.
D) ΔH° = –683.0 kJ and ΔE° = -720.0 kJ.
6) At 1 atm pressure, the heat of sublimation of gallium is 277 kJ/mol and the heat of
vaporization is 271 kJ/mol. To the correct number of significant figures, how much heat is
required to melt 2.50 mol of gallium at 1 atm pressure?
A) 6 kJ
B) 20 kJ
C) 262 kJ
D) 274 kJ
7) How much heat is absorbed/released when 35.00 g of NH3(g) reacts in the presence of excess
(g) to produce NO(g) and H2O(l) according to the following chemical equation?
4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(l) ΔH° = 1168 kJ
A) 600.1 kJ of heat are absorbed.
B) 600.1 kJ of heat are released.
C) 2400 kJ of heat are absorbed.
D) 2400 kJ of heat are released.
8) How much heat is absorbed when 45.00 g of C(s) reacts in the presence of excess SO2(g) to
produce CS2(l) and CO(g) according to the following chemical equation?
5 C(s) + 2 SO2(g) → CS2(l) + 4 CO(g) ΔH° = 239.9 kJ
A) 179.8 kJ
B) 239.9 kJ
C) 898.5 kJ
D) 2158 kJ
9) At constant pressure, the combustion of 15.0 g of C2H6(g) releases 777 kJ of heat. What is
ΔH for the reaction given below?
2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(l).
A) -129 kJ
B) -779 kJ
C) -1560 kJ
D) -3108 kJ
10) The heat of vaporization of water at 100°C is 40.66 kJ/mol. Calculate the quantity of heat
that is absorbed/released when 9.00 g of steam condenses to liquid water at 100°C.
A) 20.3 kJ of heat are absorbed.
B) 20.3 kJ of heat are released.
C) 81.3 kJ of heat are absorbed.
D) 81.3 kJ of heat are released.
11) When 1.50 mol of CH4(g) reacts with excess Cl2(g) at constant pressure according to the
chemical equation shown below, 1062 kJ of heat are released. Calculate the value of ΔH for this
reaction, as written.
2 CH4(g) + 3 Cl2(g) → 2 CHCl3(l) + 3 H2(g) ΔH = ?
A) -1420 kJ
B) -708 kJ
C) +708 kJ
D) +1420 kJ
12) Calculate the total quantity of heat required to convert 25.0 g of liquid CCl4(l) from 35.0°C
to gaseous CCl4 76.8°C (the normal boiling point for CCl4)? The specific heat of CCl4(l) is
its heat of fusion is and its heat of vaporization is
A) 0.896 kJ
B) 1.43 kJ
C) 5.74 kJ
D) 6.28 kJ
13) The specific heat of copper is 0.385 J/(g ∙ °C). If 34.2 g of copper, initially at 24.0°C, absorbs
4.689 kJ, what will be the final temperature of the copper?
A) 24.4°C
B) 26.8°C
C) 356°C
D) 380°C
14) It takes 11.2 kJ of energy to raise the temperature of 145 g of benzene from 23.0°C to
68.0°C. What is the specific heat of benzene?
A) 1.14 J/(g ∙ °C)
B) 1.72 J/(g ∙ °C)
C) 3.48 J/(g ∙ °C)
D) 5.25 J/(g ∙ °C)
15) When 1.50 g of Ba(s) is added to 100.00 g of water in a container open to the atmosphere,
the reaction shown below occurs and the temperature of the resulting solution rises from 22.00°C
to 33.10°C. If the specific heat of the solution is 4.18 J/(g ∙ °C), calculate for the reaction, as
written.
Ba(s) + 2 H2O(l) → Ba(OH)2(aq) + H2(g) = ?
A) -431 kJ
B) -3.14 kJ
C) +3.14 kJ
D) +431 kJ
16) Sodium metal reacts with water to produce hydrogen gas and sodium hydroxide according to
the chemical equation shown below. When 0.025 mol of Na is added to 100.00 g of water, the
temperature of the resulting solution rises from 25.00°C to 35.75°C. If the specific heat of the
solution is 4.18 J/(g ∙ °C), calculate ΔH for the reaction, as written.
2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g) ΔH= ?
A) -5.41 kJ
B) -90.0 kJ
C) -180 kJ
D) -364 kJ
17) When 50.0 mL of 0.400 M Ca(NO3)2 is added to 50.0 mL of 0.800 M NaF, CaF2
precipitates, as shown in the net ionic equation below. The initial temperature of both solutions is
23.0°C. Assuming that the reaction goes to completion, and that the resulting solution has a
mass of 100.00 g and a specific heat of 4.18 J/(g ∙ °C), calculate the final temperature of the
solution.
Ca2+(aq) + 2 F–(aq) → CaF2(s) ΔH° = -11.5 kJ
A) 22.45°C
B) 23.55°C
C) 24.10°C
D) 24.65°C
18) Calculate the heat of formation for CaC (s) given that ΔH for the following reaction is
+178 kJ/mole and using standard enthalpies of formation:
CaC (s) → CaO(s) + C (g)
A) -1207 kJ/mol
B) +1207 kJ/mol
C) – 851 kJ/mol
D) + 851 kJ/mol
19) When 0.455 g of anthracene, C14H10, is combusted in a bomb calorimeter that has a water
jacket containing 500.0 g of water, the temperature of the water increases by 8.63°C. Assuming
that the specific heat of water is 4.18 J/(g ∙ °C), and that the heat absorption by the calorimeter is
negligible, estimate the enthalpy of combustion per mole of anthracene.
A) +39.7 kJ/mol
B) -39.7 kJ/mol
C) -7070 kJ/mol
D) -8120 kJ/mol
20) At a given temperature and pressure, which of the following would be expected to have the
greatest molar entropy?
A) F2(s)
B) F2(l)
C) F2(g)
D) All of these would be expected to have the same molar entropy.
46
21) For the freezing of liquid bromine, Br2, at a given temperature and pressure,
A) ΔH is negative and ΔS is negative.
B) ΔH is negative and ΔS is positive.
C) ΔH is positive and ΔS is negative.
D) ΔH is positive and ΔS is positive.
8.3 Short Answer Questions
1) Energy can be classified as either ________ energy (energy of motion) or ________ energy
(stored energy).
2) Kinetic energy increases with increasing ________ and increasing ________.
3) The SI unit for energy is the ________.
4) ________ energy is the kinetic energy of molecular motion.
5) A reaction for which ΔE = – 450 kJ is one in which products have 450 kJ ________ internal
energy than the reactants, and products are ________ stable than the reactants.
6) Heat transferred in a chemical reaction or physical change is expressed as ΔE when the heat
is transferred under constant ________ and is expressed as ΔH when heat is transferred under
constant ________ conditions.
7) In the reaction shown below, ________ kJ of heat are released per mole of O2(g) that reacts.
C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g) ΔH = – 2045 kJ
8) Because the number of moles of gas are increasing from 6 to 7 in the reaction shown below, at
constant pressure ΔE is predicted to be slightly ________ negative than ΔH.
C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)
9) When 1.0 mole of MgSO4 is dissolved in water contained in a calorimeter, the temperature of
the water and dissolved ions increases. Therefore the sign of ΔH for this reaction is ________,
heat is transferred ________ the system ________ the surroundings, and the reaction is classified
as ________.
10) A spontaneous reaction has a ________ value of △G and is favored by a ________ value
of ΔH and a ________ value of ΔS.