5 TERMOQUIMICA

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UNIVERSIDADE FEDERAL DO ESTADO DO RIO DE JANEIRO (UNIRIO) 
INSTITUTO DE BIOCIÊNCIAS – DEP. DE CIÊNCIAS NATURAIS 
DISCIPLINA: QUÍMICA GERAL – 2/2016 
CURSOS: BIOMEDICINA / BACH. BIOLOGIA / LIC. BIOLOGIA 
 
LISTA DE EXERCÍCIOS TERMOQUÍMICA/TERMODINÂMICA 
 
1- Definir ou explicar: 
a) Sistema; b) Vizinhanças; c) Funções de estado; 
d) Energia interna; e) Calor; f) Entalpia; 
g) Princípio Zero da Termodinâmica; 
h) Primeira Lei da Termodinâmica; 
 
2- O calor de combustão do álcool etílico (C2H6O) e do ácido acético (C2H4O2) são - 
327 e - 210 kcal/mol, respectivamente. Qual o calor de formação do ácido acético 
a partir do álcool etílico? 
 
3- A 27 ºC o calor de combustão, a pressão constante, do propano (C3H8) é 530,6 
kcal/mol, enquanto que o calor de formação da água líquida é de 68,3 e do gás 
carbônico é 94,0 kcal/mol. Determine o calor de formação do propano, a 27 ºC, a 
pressão constante e a volume constante. 
 
4- Sabendo que os calores de formação para a amônia (NH3), ácido clorídrico (HCl) e 
cloreto de amônio (NH4Cl) são –46,1 kJ/mol; -92,3 kJ/mol e –314,4 kJ/mol, 
respectivamente, calcule ΔH0 para a seguinte reação a 25ºC: 
NH3(g) + HCl(g) → NH4Cl(s). 
 
5- Sabendo que o ΔH0 de formação da água líquida é – 68,3 kcal/mol e que para a 
formação de água no estado gasoso é de –57,8 kcal/mol, calcule o valor da 
entalpia de vaporização da água líquida em kcal/mol. 
 
6- Sabendo-se que a 25 ºC e 1 atm: calor de combustão do C(s, diamante) = - 94,6 
kcal/mol de CO2; e calor para conversão de C(s, diamante) em C(s, grafita) = - 0,5 
kcal/mol de carbono, calcule o valor do calor de combustão do C(s, grafita). 
 
7- Para os exercícios anteriores desenhe os gráficos energéticos (energia versus 
tempo) para cada uma das reações envolvidas, dizendo se os processos são 
endotérmicos ou exotérmicos. 
 
8- A reação entre o alumínio e o óxido de ferro (III), produz uma grande quantidade 
de calor. 
2 Aℓ(s) + Fe2O3(s) → Aℓ2 O3(s) + 2 Fe(s), ΔΗ = -852 kJ 
Se 10 g de Aℓ reagirem com excesso de Fe2O3, qual a quantidade de calor em kJ, que 
será liberada, a pressão constante? 
 
9- A queima parcial de carvão na presença de O2 e H2O produz uma mistura gasosa 
chamada gás de síntese, composta por de CO(g) e H2(g). Este gás de síntese pode 
ser usado como combustível e na produção de importantes compostos orgânicos, 
como por exemplo, o álcool metílico. Um gás de síntese tem a seguinte composição 
por volume: 55% CO(g), 33% H2(g), e 11% de gases não combustíveis. 
a) Quantos mol de CO(g) e H2(g) estão presentes numa amostra de 1,00 L deste gás 
nas CNTP? 
b) Qual é o calor de combustão por litro deste gás de síntese medido nas CNTP? 
 
Reações : 
Combustão do H2(g): H2(g) + ½ O2(g) → H2O(g), ΔHR = -285,8 kJ mol-1 
Combustão do CO(g): CO(g) + ½ O2(g) → CO2(g), ΔHR = - 283,0 kJ mol-1 
 
10- A combustão de 1,0 mol de metano, CH4(g), libera 820,2 kJ nas condições-padrão, 
segundo a reação: 
CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(ℓ) 
Nestas condições, calcule a variação de entalpia quando 0,5 mol de metano queima 
totalmente na presença de oxigênio. 
 
11- Quando alumínio metálico é exposto ao oxigênio atmosférico (como em portas e 
janelas de alumínio), ele é oxidado a óxido de alumínio conforme a reação abaixo. 
Quanto de calor é liberado pela completa oxidação de 24,2 g de alumínio a 25 ºC e 1 
atm? 
4Al(s) + 3O2(g) → 2Al2O3(s) ΔH = – 3352 kJ/mol 
 
 
 
 
 
 
 
 
 
638 CHAPTER 15: Chemical Thermodynamics
PbCl2(s); (c) atomic oxygen, O(g); (d) benzoic acid,
C6H5COOH(s); (e) hydrogen peroxide, H2O2(!); 
(f ) dinitrogen tetroxide, N2O4(g).
0*28. We burn 14.4 g of lithium in excess oxygen at constant
atmospheric pressure to form Li2O. Then we bring the
reaction mixture back to 25°C. In this process 605 kJ of
heat is given off. What is the standard molar enthalpy of
formation of Li2O?
0*29. We burn 14.4 g of magnesium in excess nitrogen at con-
stant atmospheric pressure to form Mg3N2. Then we
bring the reaction mixture back to 25°C. In this process
136.7 kJ of heat is given off. What is the standard molar
enthalpy of formation of Mg3N2?
*030. From the following enthalpies of reaction,
4HCl(g) !O2(g) 88n 2H2O(!)! 2Cl2(g)
"H#$202.4 kJ/mol rxn
%12%H2(g) ! %
1
2%F2(g) 88n HF(!)
"H#$600.0 kJ/mol rxn
H2(g) ! %
1
2%O2(g) 88n H2O(!)
"H#$285.8 kJ/mol rxn
find "Hrxn for 2HCl(g)! F2(g) 88n 2HF(!) ! Cl2(g).
*031. From the following enthalpies of reaction,
CaCO3(s) 88n CaO(s)! CO2(g)
"H#!178.1 kJ/mol rxn
CaO(s) !H2O(!) 88n Ca(OH)2(s)
"H #$65.3 kJ/mol rxn
Ca(OH)2(s) 88n Ca2!(aq) ! 2OH$(aq)
"H #$16.2 kJ/mol rxn
calculate "Hrxn for
Ca2!(aq)! 2OH$(aq) ! CO2(g) 88n
CaCO3(s) !H2O(!)
*032. Given that
S(s)!O2(g) 88n SO2(g) "H# $296.8 kJ/mol
S(s) ! %32%O2(g) 88n SO3(g) "H# $395.6 kJ/mol
determine the enthalpy change for the decomposition
reaction 2SO3(g) n 2SO2(g) !O2(g).
*033. Aluminum reacts vigorously with many oxidizing agents.
For example,
4Al(s)! 3O2(g) 88n 2Al2O3(s)
"H #$3352 kJ/mol
4Al(s)! 3MnO2(s) 88n 3Mn(s)! 2Al2O3(s)
"H #$1792 kJ/mol
Use this information to determine the enthalpy of for-
mation of MnO2(s).
*034. Given that
2H2(g) !O2(g) 88n 2H2O(!)
"H#$571.6 kJ/mol
C3H4(g) ! 4O2(g) 88n 3CO2(g) ! 2H2O(!)
"H#$1937 kJ/mol.
C3H8(g) ! 5O2(g) 88n 3CO2(g) ! 4H2O(!)
"H#$2220 kJ/mol.
determine the heat of the hydrogenation reaction
C3H4(g)! 2H2(g) 88n C3H8(g)
*035. Determine the heat of formation of liquid hydrogen per-
oxide at 25°C from the following thermochemical
equations.
H2(g) ! %
1
2%O2(g) 88n H2O(g)
"H0# 2$241.82 kJ/mol
2H(g)!O(g) 88n H2O(g)
"H0# 2$926.92 kJ/mol
2H(g)! 2O(g) 88n H2O2(g)
"H0#$1070.60 kJ/mol
2O(g) 88n O2(g)
"H0# 2$498.34 kJ/mol
H2O2(!) 88n H2O2(g)
"H0#$2251.46 kJ/mol
*036. Use data in Appendix K to find the enthalpy of reaction
for
(a) NH4NO3(s) 88n N2O(g) ! 2H2O(g)
(b) 2FeS2(s) ! %
1
2
1%O2(g) 88n Fe2O3(s) ! 4SO2(g)
(c) SiO2(s)! 3C(s) 88n SiC(s)! 2CO(g)
*037. Repeat Exercise 36 for
(a) CaCO3(s) 88n CaO(s) ! CO2(g)
(b) 2HI(g) ! F2(g) 88n 2HF(g)! I2(s)
(c) SF6(g) ! 3H2O(!) 88n 6HF(g) ! SO3(g)
*038. The internal combustion engine uses heat produced dur-
ing the burning of a fuel. Propane, C3H8(g), is sometimes
used as the fuel. Gasoline is the most commonly used fuel.
Assume that the gasoline is pure octane, C8H18(!) and
the fuel and oxygen are completely converted into CO2(g)
and H2O(g). For each of these fuels, determine the heat
released per gram of fuel burned.
*039. Propane, C3H8(g), is used as the fuel for some modern
internal combustion engines. Methane, CH4(g), has been
proposed by the movie industry as the post-Apocalypse
fuel when gasoline and propane are supposedly no longer
available. Assume that the fuel and oxygen are completely
converted into CO2(g) and H2O(g). For each of these
fuels determine the heat released per gram of fuel burned.
Compare your answers to the answers for Exercise 38.
638 CHAPTER 15: Chemical Thermodynamics
PbCl2(s); (c) atomic oxygen, O(g); (d) benzoic acid,
C6H5COOH(s); (e) hydrogen peroxide, H2O2(!); 
(f ) dinitrogen tetroxide, N2O4(g).
0*28. We burn 14.4 g of lithium in excess oxygen at constant
atmospheric pressure to form Li2O. Then we bring the
reaction mixture back to 25°C. In this process 605 kJ of
heat is given off. What is the standard molar enthalpy of
formation of Li2O?
0*29. We burn 14.4 g of magnesium in excess nitrogen at con-
stant atmospheric pressure to form Mg3N2. Then we
bring the reaction mixture back to 25°C. In this process
136.7 kJ of heat is given off. What is the standard molar
enthalpy of formation of Mg3N2?
*030. From the following enthalpies of reaction,
4HCl(g) !O2(g) 88n 2H2O(!)! 2Cl2(g)
"H#$202.4 kJ/mol rxn%12%H2(g) ! %
1
2%F2(g) 88n HF(!)
"H#$600.0 kJ/mol rxn
H2(g) ! %
1
2%O2(g) 88n H2O(!)
"H#$285.8 kJ/mol rxn
find "Hrxn for 2HCl(g)! F2(g) 88n 2HF(!) ! Cl2(g).
*031. From the following enthalpies of reaction,
CaCO3(s) 88n CaO(s)! CO2(g)
"H#!178.1 kJ/mol rxn
CaO(s) !H2O(!) 88n Ca(OH)2(s)
"H #$65.3 kJ/mol rxn
Ca(OH)2(s) 88n Ca2!(aq) ! 2OH$(aq)
"H #$16.2 kJ/mol rxn
calculate "Hrxn for
Ca2!(aq)! 2OH$(aq) ! CO2(g) 88n
CaCO3(s) !H2O(!)
*032. Given that
S(s) !O2(g) 88n SO2(g) "H# $296.8 kJ/mol
S(s)! %32%O2(g) 88n SO3(g) "H# $395.6 kJ/mol
determine the enthalpy change for the decomposition
reaction 2SO3(g) n 2SO2(g) !O2(g).
*033. Aluminum reacts vigorously with many oxidizing agents.
For example,
4Al(s)! 3O2(g) 88n 2Al2O3(s)
"H #$3352 kJ/mol
4Al(s)! 3MnO2(s) 88n 3Mn(s)! 2Al2O3(s)
"H #$1792 kJ/mol
Use this information to determine the enthalpy of for-
mation of MnO2(s).
*034. Given that
2H2(g) !O2(g) 88n 2H2O(!)
"H#$571.6 kJ/mol
C3H4(g) ! 4O2(g) 88n 3CO2(g) ! 2H2O(!)
"H#$1937 kJ/mol.
C3H8(g) ! 5O2(g) 88n 3CO2(g) ! 4H2O(!)
"H#$2220 kJ/mol.
determine the heat of the hydrogenation reaction
C3H4(g)! 2H2(g) 88n C3H8(g)
*035. Determine the heat of formation of liquid hydrogen per-
oxide at 25°C from the following thermochemical
equations.
H2(g) ! %
1
2%O2(g) 88n H2O(g)
"H0# 2$241.82 kJ/mol
2H(g)!O(g) 88n H2O(g)
"H0# 2$926.92 kJ/mol
2H(g)! 2O(g) 88n H2O2(g)
"H0#$1070.60 kJ/mol
2O(g) 88n O2(g)
"H0# 2$498.34 kJ/mol
H2O2(!) 88n H2O2(g)
"H0#$2251.46 kJ/mol
*036. Use data in Appendix K to find the enthalpy of reaction
for
(a) NH4NO3(s) 88n N2O(g) ! 2H2O(g)
(b) 2FeS2(s) ! %
1
2
1%O2(g) 88n Fe2O3(s) ! 4SO2(g)
(c) SiO2(s)! 3C(s) 88n SiC(s)! 2CO(g)
*037. Repeat Exercise 36 for
(a) CaCO3(s) 88n CaO(s) ! CO2(g)
(b) 2HI(g) ! F2(g) 88n 2HF(g)! I2(s)
(c) SF6(g) ! 3H2O(!) 88n 6HF(g) ! SO3(g)
*038. The internal combustion engine uses heat produced dur-
ing the burning of a fuel. Propane, C3H8(g), is sometimes
used as the fuel. Gasoline is the most commonly used fuel.
Assume that the gasoline is pure octane, C8H18(!) and
the fuel and oxygen are completely converted into CO2(g)
and H2O(g). For each of these fuels, determine the heat
released per gram of fuel burned.
*039. Propane, C3H8(g), is used as the fuel for some modern
internal combustion engines. Methane, CH4(g), has been
proposed by the movie industry as the post-Apocalypse
fuel when gasoline and propane are supposedly no longer
available. Assume that the fuel and oxygen are completely
converted into CO2(g) and H2O(g). For each of these
fuels determine the heat released per gram of fuel burned.
Compare your answers to the answers for Exercise 38.
 
 
 
 
 
 
 
 
 
 
638 CHAPTER 15: Chemical Thermodynamics
PbCl2(s); (c) atomic oxygen, O(g); (d) benzoic acid,
C6H5COOH(s); (e) hydrogen peroxide, H2O2(!); 
(f ) dinitrogen tetroxide, N2O4(g).
0*28. We burn 14.4 g of lithium in excess oxygen at constant
atmospheric pressure to form Li2O. Then we bring the
reaction mixture back to 25°C. In this process 605 kJ of
heat is given off. What is the standard molar enthalpy of
formation of Li2O?
0*29. We burn 14.4 g of magnesium in excess nitrogen at con-
stant atmospheric pressure to form Mg3N2. Then we
bring the reaction mixture back to 25°C. In this process
136.7 kJ of heat is given off. What is the standard molar
enthalpy of formation of Mg3N2?
*030. From the following enthalpies of reaction,
4HCl(g) !O2(g) 88n 2H2O(!)! 2Cl2(g)
"H#$202.4 kJ/mol rxn
%12%H2(g) ! %
1
2%F2(g) 88n HF(!)
"H#$600.0 kJ/mol rxn
H2(g) ! %
1
2%O2(g) 88n H2O(!)
"H#$285.8 kJ/mol rxn
find "Hrxn for 2HCl(g)! F2(g) 88n 2HF(!) ! Cl2(g).
*031. From the following enthalpies of reaction,
CaCO3(s) 88n CaO(s)! CO2(g)
"H#!178.1 kJ/mol rxn
CaO(s) !H2O(!) 88n Ca(OH)2(s)
"H #$65.3 kJ/mol rxn
Ca(OH)2(s) 88n Ca2!(aq) ! 2OH$(aq)
"H #$16.2 kJ/mol rxn
calculate "Hrxn for
Ca2!(aq)! 2OH$(aq) ! CO2(g) 88n
CaCO3(s) !H2O(!)
*032. Given that
S(s) !O2(g) 88n SO2(g) "H# $296.8 kJ/mol
S(s)! %32%O2(g) 88n SO3(g) "H# $395.6 kJ/mol
determine the enthalpy change for the decomposition
reaction 2SO3(g) n 2SO2(g) !O2(g).
*033. Aluminum reacts vigorously with many oxidizing agents.
For example,
4Al(s)! 3O2(g) 88n 2Al2O3(s)
"H #$3352 kJ/mol
4Al(s)! 3MnO2(s) 88n 3Mn(s)! 2Al2O3(s)
"H #$1792 kJ/mol
Use this information to determine the enthalpy of for-
mation of MnO2(s).
*034. Given that
2H2(g) !O2(g) 88n 2H2O(!)
"H#$571.6 kJ/mol
C3H4(g) ! 4O2(g) 88n 3CO2(g) ! 2H2O(!)
"H#$1937 kJ/mol.
C3H8(g) ! 5O2(g) 88n 3CO2(g) ! 4H2O(!)
"H#$2220 kJ/mol.
determine the heat of the hydrogenation reaction
C3H4(g)! 2H2(g) 88n C3H8(g)
*035. Determine the heat of formation of liquid hydrogen per-
oxide at 25°C from the following thermochemical
equations.
H2(g) ! %
1
2%O2(g) 88n H2O(g)
"H0# 2$241.82 kJ/mol
2H(g)!O(g) 88n H2O(g)
"H0# 2$926.92 kJ/mol
2H(g)! 2O(g) 88n H2O2(g)
"H0#$1070.60 kJ/mol
2O(g) 88n O2(g)
"H0# 2$498.34 kJ/mol
H2O2(!) 88n H2O2(g)
"H0#$2251.46 kJ/mol
*036. Use data in Appendix K to find the enthalpy of reaction
for
(a) NH4NO3(s) 88n N2O(g) ! 2H2O(g)
(b) 2FeS2(s) ! %
1
2
1%O2(g) 88n Fe2O3(s) ! 4SO2(g)
(c) SiO2(s)! 3C(s) 88n SiC(s)! 2CO(g)
*037. Repeat Exercise 36 for
(a) CaCO3(s) 88n CaO(s) ! CO2(g)
(b) 2HI(g) ! F2(g) 88n 2HF(g)! I2(s)
(c) SF6(g) ! 3H2O(!) 88n 6HF(g) ! SO3(g)
*038. The internal combustion engine uses heat produced dur-
ing the burning of a fuel. Propane, C3H8(g), is sometimes
used as the fuel. Gasoline is the most commonly used fuel.
Assume that the gasoline is pure octane, C8H18(!) and
the fuel and oxygen are completely converted into CO2(g)
and H2O(g). For each of these fuels, determine the heat
released per gram of fuel burned.
*039. Propane, C3H8(g), is used as the fuel for some modern
internal combustion engines. Methane, CH4(g), has been
proposed by the movie industry as the post-Apocalypse
fuel when gasoline and propane are supposedly no longer
available. Assume that the fuel and oxygen are completely
converted into CO2(g) and H2O(g). For each of these
fuels determine the heat released per gram of fuel burned.
Compare your answers to the answers for Exercise 38.
638 CHAPTER 15: Chemical Thermodynamics
PbCl2(s); (c) atomic oxygen, O(g); (d) benzoic acid,
C6H5COOH(s); (e) hydrogen peroxide, H2O2(!); 
(f ) dinitrogen tetroxide, N2O4(g).
0*28. We burn 14.4 g of lithium in excess oxygen at constant
atmospheric pressure to form Li2O. Then we bring the
reaction mixture back to 25°C. In this process 605 kJ of
heat is given off. What is the standard molar enthalpy of
formation of Li2O?
0*29. We burn 14.4 g of magnesium in excess nitrogen at con-
stant atmospheric pressure to form Mg3N2. Then we
bring the reaction mixture back to 25°C. In this process
136.7 kJ of heat is given off. What is the standard molar
enthalpy of formation of Mg3N2?
*030. From the following enthalpies of reaction,
4HCl(g) !O2(g) 88n 2H2O(!)! 2Cl2(g)
"H#$202.4 kJ/mol rxn
%12%H2(g) ! %
1
2%F2(g) 88n HF(!)
"H#$600.0 kJ/mol rxn
H2(g) ! %
1
2%O2(g) 88n H2O(!)
"H#$285.8 kJ/mol rxn
find "Hrxn for 2HCl(g)! F2(g) 88n 2HF(!) ! Cl2(g).
*031. From the following enthalpies of reaction,
CaCO3(s) 88n CaO(s)! CO2(g)
"H#!178.1 kJ/mol rxn
CaO(s) !H2O(!) 88n Ca(OH)2(s)
"H #$65.3 kJ/mol rxn
Ca(OH)2(s) 88n Ca2!(aq) ! 2OH$(aq)
"H #$16.2 kJ/mol rxn
calculate "Hrxn for
Ca2!(aq)! 2OH$(aq) ! CO2(g) 88n
CaCO3(s) !H2O(!)
*032. Given that
S(s)!O2(g) 88n SO2(g) "H# $296.8 kJ/mol
S(s)! %32%O2(g) 88n SO3(g) "H# $395.6 kJ/mol
determine the enthalpy change for the decomposition
reaction 2SO3(g) n 2SO2(g) !O2(g).
*033. Aluminum reacts vigorously with many oxidizing agents.
For example,
4Al(s)! 3O2(g) 88n 2Al2O3(s)
"H #$3352 kJ/mol
4Al(s)! 3MnO2(s) 88n3Mn(s)! 2Al2O3(s)
"H #$1792 kJ/mol
Use this information to determine the enthalpy of for-
mation of MnO2(s).
*034. Given that
2H2(g) !O2(g) 88n 2H2O(!)
"H#$571.6 kJ/mol
C3H4(g) ! 4O2(g) 88n 3CO2(g) ! 2H2O(!)
"H#$1937 kJ/mol.
C3H8(g) ! 5O2(g) 88n 3CO2(g) ! 4H2O(!)
"H#$2220 kJ/mol.
determine the heat of the hydrogenation reaction
C3H4(g)! 2H2(g) 88n C3H8(g)
*035. Determine the heat of formation of liquid hydrogen per-
oxide at 25°C from the following thermochemical
equations.
H2(g) ! %
1
2%O2(g) 88n H2O(g)
"H0# 2$241.82 kJ/mol
2H(g)!O(g) 88n H2O(g)
"H0# 2$926.92 kJ/mol
2H(g)! 2O(g) 88n H2O2(g)
"H0#$1070.60 kJ/mol
2O(g) 88n O2(g)
"H0# 2$498.34 kJ/mol
H2O2(!) 88n H2O2(g)
"H0#$2251.46 kJ/mol
*036. Use data in Appendix K to find the enthalpy of reaction
for
(a) NH4NO3(s) 88n N2O(g) ! 2H2O(g)
(b) 2FeS2(s) ! %
1
2
1%O2(g) 88n Fe2O3(s) ! 4SO2(g)
(c) SiO2(s)! 3C(s) 88n SiC(s)! 2CO(g)
*037. Repeat Exercise 36 for
(a) CaCO3(s) 88n CaO(s) ! CO2(g)
(b) 2HI(g) ! F2(g) 88n 2HF(g)! I2(s)
(c) SF6(g) ! 3H2O(!) 88n 6HF(g) ! SO3(g)
*038. The internal combustion engine uses heat produced dur-
ing the burning of a fuel. Propane, C3H8(g), is sometimes
used as the fuel. Gasoline is the most commonly used fuel.
Assume that the gasoline is pure octane, C8H18(!) and
the fuel and oxygen are completely converted into CO2(g)
and H2O(g). For each of these fuels, determine the heat
released per gram of fuel burned.
*039. Propane, C3H8(g), is used as the fuel for some modern
internal combustion engines. Methane, CH4(g), has been
proposed by the movie industry as the post-Apocalypse
fuel when gasoline and propane are supposedly no longer
available. Assume that the fuel and oxygen are completely
converted into CO2(g) and H2O(g). For each of these
fuels determine the heat released per gram of fuel burned.
Compare your answers to the answers for Exercise 38.
638 CHAPTER 15: Chemical Thermodynamics
PbCl2(s); (c) atomic oxygen, O(g); (d) benzoic acid,
C6H5COOH(s); (e) hydrogen peroxide, H2O2(!); 
(f ) dinitrogen tetroxide, N2O4(g).
0*28. We burn 14.4 g of lithium in excess oxygen at constant
atmospheric pressure to form Li2O. Then we bring the
reaction mixture back to 25°C. In this process 605 kJ of
heat is given off. What is the standard molar enthalpy of
formation of Li2O?
0*29. We burn 14.4 g of magnesium in excess nitrogen at con-
stant atmospheric pressure to form Mg3N2. Then we
bring the reaction mixture back to 25°C. In this process
136.7 kJ of heat is given off. What is the standard molar
enthalpy of formation of Mg3N2?
*030. From the following enthalpies of reaction,
4HCl(g) !O2(g) 88n 2H2O(!)! 2Cl2(g)
"H#$202.4 kJ/mol rxn
%12%H2(g) ! %
1
2%F2(g) 88n HF(!)
"H#$600.0 kJ/mol rxn
H2(g) ! %
1
2%O2(g) 88n H2O(!)
"H#$285.8 kJ/mol rxn
find "Hrxn for 2HCl(g)! F2(g) 88n 2HF(!) ! Cl2(g).
*031. From the following enthalpies of reaction,
CaCO3(s) 88n CaO(s)! CO2(g)
"H#!178.1 kJ/mol rxn
CaO(s) !H2O(!) 88n Ca(OH)2(s)
"H #$65.3 kJ/mol rxn
Ca(OH)2(s) 88n Ca2!(aq) ! 2OH$(aq)
"H #$16.2 kJ/mol rxn
calculate "Hrxn for
Ca2!(aq)! 2OH$(aq) ! CO2(g) 88n
CaCO3(s) !H2O(!)
*032. Given that
S(s)!O2(g) 88n SO2(g) "H# $296.8 kJ/mol
S(s) ! %32%O2(g) 88n SO3(g) "H# $395.6 kJ/mol
determine the enthalpy change for the decomposition
reaction 2SO3(g) n 2SO2(g) !O2(g).
*033. Aluminum reacts vigorously with many oxidizing agents.
For example,
4Al(s)! 3O2(g) 88n 2Al2O3(s)
"H #$3352 kJ/mol
4Al(s)! 3MnO2(s) 88n 3Mn(s)! 2Al2O3(s)
"H #$1792 kJ/mol
Use this information to determine the enthalpy of for-
mation of MnO2(s).
*034. Given that
2H2(g) !O2(g) 88n 2H2O(!)
"H#$571.6 kJ/mol
C3H4(g) ! 4O2(g) 88n 3CO2(g) ! 2H2O(!)
"H#$1937 kJ/mol.
C3H8(g) ! 5O2(g) 88n 3CO2(g) ! 4H2O(!)
"H#$2220 kJ/mol.
determine the heat of the hydrogenation reaction
C3H4(g)! 2H2(g) 88n C3H8(g)
*035. Determine the heat of formation of liquid hydrogen per-
oxide at 25°C from the following thermochemical
equations.
H2(g) ! %
1
2%O2(g) 88n H2O(g)
"H0# 2$241.82 kJ/mol
2H(g)!O(g) 88n H2O(g)
"H0# 2$926.92 kJ/mol
2H(g)! 2O(g) 88n H2O2(g)
"H0#$1070.60 kJ/mol
2O(g) 88n O2(g)
"H0# 2$498.34 kJ/mol
H2O2(!) 88n H2O2(g)
"H0#$2251.46 kJ/mol
*036. Use data in Appendix K to find the enthalpy of reaction
for
(a) NH4NO3(s) 88n N2O(g) ! 2H2O(g)
(b) 2FeS2(s) ! %
1
2
1%O2(g) 88n Fe2O3(s) ! 4SO2(g)
(c) SiO2(s)! 3C(s) 88n SiC(s)! 2CO(g)
*037. Repeat Exercise 36 for
(a) CaCO3(s) 88n CaO(s) ! CO2(g)
(b) 2HI(g) ! F2(g) 88n 2HF(g)! I2(s)
(c) SF6(g) ! 3H2O(!) 88n 6HF(g) ! SO3(g)
*038. The internal combustion engine uses heat produced dur-
ing the burning of a fuel. Propane, C3H8(g), is sometimes
used as the fuel. Gasoline is the most commonly used fuel.
Assume that the gasoline is pure octane, C8H18(!) and
the fuel and oxygen are completely converted into CO2(g)
and H2O(g). For each of these fuels, determine the heat
released per gram of fuel burned.
*039. Propane, C3H8(g), is used as the fuel for some modern
internal combustion engines. Methane, CH4(g), has been
proposed by the movie industry as the post-Apocalypse
fuel when gasoline and propane are supposedly no longer
available. Assume that the fuel and oxygen are completely
converted into CO2(g) and H2O(g). For each of these
fuels determine the heat released per gram of fuel burned.
Compare your answers to the answers for Exercise 38.
 
638 CHAPTER 15: Chemical Thermodynamics
PbCl2(s); (c) atomic oxygen, O(g); (d) benzoic acid,
C6H5COOH(s); (e) hydrogen peroxide, H2O2(!); 
(f ) dinitrogen tetroxide, N2O4(g).
0*28. We burn 14.4 g of lithium in excess oxygen at constant
atmospheric pressure to form Li2O. Then we bring the
reaction mixture back to 25°C. In this process 605 kJ of
heat is given off. What is the standard molar enthalpy of
formation of Li2O?
0*29. We burn 14.4 g of magnesium in excess nitrogen at con-
stant atmospheric pressure to form Mg3N2. Then we
bring the reaction mixture back to 25°C. In this process
136.7 kJ of heat is given off. What is the standard molar
enthalpy of formation of Mg3N2?
*030. From the following enthalpies of reaction,
4HCl(g) !O2(g) 88n 2H2O(!)! 2Cl2(g)
"H#$202.4 kJ/mol rxn
%12%H2(g) ! %
1
2%F2(g) 88n HF(!)
"H#$600.0 kJ/mol rxn
H2(g) ! %
1
2%O2(g) 88n H2O(!)
"H#$285.8 kJ/mol rxn
find "Hrxn for 2HCl(g)! F2(g) 88n 2HF(!) ! Cl2(g).
*031. From the following enthalpies of reaction,
CaCO3(s) 88n CaO(s)! CO2(g)
"H#!178.1 kJ/mol rxn
CaO(s) !H2O(!) 88n Ca(OH)2(s)
"H #$65.3 kJ/mol rxn
Ca(OH)2(s) 88n Ca2!(aq) ! 2OH$(aq)
"H #$16.2 kJ/mol rxn
calculate "Hrxn for
Ca2!(aq)! 2OH$(aq) ! CO2(g) 88n
CaCO3(s) !H2O(!)
*032. Given that
S(s)!O2(g) 88n SO2(g) "H# $296.8 kJ/mol
S(s)! %32%O2(g) 88n SO3(g) "H# $395.6 kJ/mol
determine the enthalpy change for the decomposition
reaction 2SO3(g) n 2SO2(g) !O2(g).
*033. Aluminum reacts vigorously with many oxidizing agents.
For example,
4Al(s)! 3O2(g) 88n 2Al2O3(s)
"H #$3352 kJ/mol
4Al(s)! 3MnO2(s) 88n 3Mn(s)! 2Al2O3(s)
"H #$1792 kJ/mol
Use this information to determine the enthalpy of for-
mation of MnO2(s).
*034. Given that
2H2(g) !O2(g) 88n 2H2O(!)
"H#$571.6 kJ/mol
C3H4(g) ! 4O2(g) 88n 3CO2(g) ! 2H2O(!)
"H#$1937 kJ/mol.
C3H8(g) ! 5O2(g) 88n 3CO2(g) ! 4H2O(!)
"H#$2220 kJ/mol.
determine the heat of the hydrogenation reaction
C3H4(g)! 2H2(g) 88n C3H8(g)
*035. Determine the heat of formation of liquid hydrogen per-
oxide at 25°C from the following thermochemical
equations.
H2(g) ! %
1
2%O2(g) 88n H2O(g)
"H0# 2$241.82 kJ/mol
2H(g)!O(g) 88n H2O(g)
"H0# 2$926.92 kJ/mol
2H(g)! 2O(g) 88n H2O2(g)
"H0#$1070.60 kJ/mol
2O(g) 88n O2(g)
"H0# 2$498.34 kJ/mol
H2O2(!) 88n H2O2(g)
"H0#$2251.46 kJ/mol
*036. Use data in Appendix K to find the enthalpy of reaction
for
(a) NH4NO3(s) 88n N2O(g) ! 2H2O(g)
(b) 2FeS2(s)! %
1
2
1%O2(g) 88n Fe2O3(s) ! 4SO2(g)
(c) SiO2(s)! 3C(s) 88n SiC(s)! 2CO(g)
*037. Repeat Exercise 36 for
(a) CaCO3(s) 88n CaO(s) ! CO2(g)
(b) 2HI(g) ! F2(g) 88n 2HF(g)! I2(s)
(c) SF6(g) ! 3H2O(!) 88n 6HF(g) ! SO3(g)
*038. The internal combustion engine uses heat produced dur-
ing the burning of a fuel. Propane, C3H8(g), is sometimes
used as the fuel. Gasoline is the most commonly used fuel.
Assume that the gasoline is pure octane, C8H18(!) and
the fuel and oxygen are completely converted into CO2(g)
and H2O(g). For each of these fuels, determine the heat
released per gram of fuel burned.
*039. Propane, C3H8(g), is used as the fuel for some modern
internal combustion engines. Methane, CH4(g), has been
proposed by the movie industry as the post-Apocalypse
fuel when gasoline and propane are supposedly no longer
available. Assume that the fuel and oxygen are completely
converted into CO2(g) and H2O(g). For each of these
fuels determine the heat released per gram of fuel burned.
Compare your answers to the answers for Exercise 38.