Modern Engineering Thermodynamics

648 CHAPTER 15: Chemical Thermodynamics
Table 15.11 Problem 50
Component Molecular Mass %
N 2 28.0 77.4
O 2 32.0 13.6
H 2 O 18.0 4.5
CO 2 44.0 4.5
Total 100.0
An exhaust gas analysis of the products of this combustion
yielded the Table 15.11 percentage composition on a volume
basis. Using these data, determine
a. The temperature to which the exhaust must be cooled to
cause the water vapor to condense, if the exhaust is at a total
pressure of 22.223 psia.
b. The amount of excess air x used in the combustion process.
c. The air/fuel ratio on a mass basis.
In Problems 51 through 55, use Eqs. (15.4), (15.6), and the
higher heating value data given in Table 15.2 to compute the
molar specific enthalpy of formation at the standard
reference state, h° f , of each compound from its
compound
elements. Compare your results with the values given in
Table 15.1.
51. Acetylene: 2½CðsÞŠ + H 2 ðgÞ !C 2 H 2 ðgÞ + ðq°Þ ,ðh° f C2H2ðgÞ f Þ = ?
C2H2ðgÞ
52. Ethylene: 2½CðsÞŠ+2½H 2 ðgÞŠ ! C 2 H 4 ðgÞ+ðq°Þ ,ðh° f C2H4ðgÞ f Þ = ?
C2H4ðgÞ
53. Propane: 3½CðsÞŠ+3½H 2 ðgÞŠ ! C 3 H 6 ðgÞ+ðq°Þ ,ðh° f C3H6ðgÞ f Þ = ?
C3H6ðgÞ
54. Ethane: 2½CðsÞŠ + 3½H 2 ðgÞŠ ! C 2 H 6 ðgÞ + ðq°Þ , ðh° f C2H6ðgÞ f Þ = ?
C2H6ðgÞ
55. Butane: 4½CðsÞŠ+5½H 2 ðgÞŠ ! C 4 H 10 ðgÞ+ðq°Þ ,ðh° f C4H10ðgÞ f Þ = ?
C4H10ðgÞ
56. Repeat Example 15.8 using 150.% theoretical air.
57. Repeat Example 15.8 using 90.0% theoretical air. Assume the
hydrogen is much more reactive than the carbon and is all
converted into water.
58. Repeat Example 15.9 using 150.% theoretical air in the
combustion process.
59.* The higher heating value of glucose, C 6 H 12 O 6 ðsÞ, is
−2817:5 MJ/kgmole: Determine the standard reference state
molar specific enthalpy of formation of glucose using the reaction
C 6 H 12 O 6 ðsÞ + 6½O 2 ðgÞŠ ! 6½CO 2 ðgÞŠ + 6½H 2
OðlÞŠ
60. Determine the heat of combustion of propane (C 3 H 8 ) gas with
100.% theoretical air when the reactants are at the standard
reference state, but the products are at 2000. R. Use the gas
tables in Thermodynamic Tables to accompany Modern Engineering
Thermodynamics (Table C.16c).
61. Using the gas tables, Table C.16c, determine the heat of
combustion of liquid octane, C 8 H 18 (l), with 200.% theoretical
air when the reactants are at 537 R and the products are at
4000. R. Explain the significance of your answer.
62. Liquid ethyl alcohol at 77.0°F is burned in 100.% theoretical air.
Determine the heat produced per kgmole of fuel when the
products are at 540.°F. The molar specific enthalpy of formation
of this fuel is − 277:69 MJ/kgmole:
63.* Methane gas (CH 4 )at−60.0°C is burned during a severe winter
with 200.% theoretical air at the same temperature. The
products of combustion are at 300.°C. Assuming constant
specific heats, find the heat released per kgmole of fuel.
64. Kerosene (decane, C 10 H 22 ) with a density of 49.3 lbm/ft 3 has a
HHV of 20,484 Btu/lbm and costs $0.500 per gallon. Calculate
the cost of 1.00 therm (10 5 Btu) obtained by burning kerosene.
65.* The explosive energy of a high explosive is defined to be the lower
heating value (LHV) of the detonation reaction. The heat of
formation of nitroglycerin, C 3 H 5 ðNO 3 Þ 3 ,is−354 MJ/kgmole,
and its molecular mass is 227 kg/kgmole.
a. Find the values of a, b, c, and d in the following reaction
describing the detonation of nitroglycerin:
C 3 H 5 ðNO 3 Þ 3
! aðCO 2 Þ + bðH 2 OÞ + cðO 2 Þ + dðN 2 Þ
b. Determine the explosive energy of nitroglycerin in MJ/kg.
66.* In Problem 65, the explosive energy of a high explosive was
defined to be the lower heating value (LHV) of the detonation
reaction. The heat of formation of trinitrotoluene (TNT),
C 7 H 5 ðNO 2 Þ 3 ,is−54.4 MJ/kgmole, and its molecular mass is
227 kg/kgmole.
a. Find the values of a, b, c, and d in the following simplified
reaction describing the detonation of TNT:
C 7 H 5 ðNO 2 Þ 3 ! aðCOÞ + bðCH 4 Þ + cðH 2 OÞ + dðN 2 Þ
b. Determine the explosive energy of TNT in MJ/kg.
67. Determine the adiabatic flame temperature of methane (CH 4 )
burned in 400.% theoretical air in a steady flow process.
68. Determine the adiabatic flame temperature of acetylene
(C 2 H 2 ) burned in a steady flow process with (a) 100.%
theoretical air, (b) 200.% theoretical air, and (c) 400.%
theoretical air.
69. Determine the adiabatic flame temperature of propane (C 3 H 6 )
burned in a steady flow process with (a) 0.00% excess air,
(b) 100.% excess air, and (c) 300.% excess air.
70. Determine the adiabatic flame temperature of benzene (C 6 H 6 )
burned in a steady flow process with (a) 0.00% excess air,
(b) 100.% excess air, and (c) 300.% excess air.
71.* Determine the adiabatic flame temperature and maximum
explosion pressure as 0.001 kgmole of butane (C 4 H 10 ) is burned
in 100.% theoretical air in a 0.100 m 3 adiabatic bomb
calorimeter.
72.* Determine the molar specific entropy production ðs P Þ r
for the
reaction C + O 2 ! CO 2 , when both the products and the
reactants are at the standard reference state. Assume an
isothermal boundary at 298 K.
73.* Determine the molar specific entropy production ðs P Þ r for the
combustion of methane in pure oxygen,
CH 4 + 2ðO 2 Þ!CO 2 + 2ðH 2 OÞ, when both the products and the
reactants are at the standard reference state. Assume an
isothermal boundary at 298 K.
74.* Determine the molar specific entropy production ðs P Þ r
as
ethylene is burned in an adiabatic combustion chamber with
100.% theoretical air. The reactants are at the standard reference
state, but the products are at 5.00 MPa. The adiabatic flame
temperature is 2291.6°C. Assume constant specific heats
(Table C.13b).
75. Using the gas tables (Table C.16c), determine the molar specific
entropy production ðs P Þ r
for the combustion of propane with
100.% theoretical air. The reactants are at the standard reference
state. The products are at 2000. R and 4.00 MPa, and the
heat transfer from the combustion chamber is 571,126 Btu/
(lbmole·R). Assume the combustion chamber has isothermal
walls at 2000. R.
76. Determine the molar specific entropy of formation s f ° for (a)
CO, (b) CO 2 , and (c) H 2 O.