Question

The standard heat of formation, Δ*H*∘f, is defined as the
enthalpy change for the formation of one mole of substance from its
constituent elements in their standard states. Thus, elements in
their standard states have Δ*H*∘f=0. Heat of formation
values can be used to calculate the enthalpy change of any
reaction.

Consider, for example, the reaction

2NO(g)+O2(g)⇌2NO2(g)

with heat of formation values given by the following table:

Substance |
ΔH∘f(kJ/mol) |

NO(g) | 90.2 |

O2(g) | 0 |

NO2(g) | 33.2 |

Then the heat of formation for the overall reaction is

Δ*H*∘rxn===Δ*H*∘f(products)2(33.2)−114
kJ/mol−−Δ*H*∘f(reactants)[2(90.2)+0]

For which of the following reactions is Δ*H*∘rxn equal to
Δ*H*∘f of the product(s)?

You do *not* need to look up any values to answer this
question.

Check all that apply.

**View Available Hint(s)**

Check all that apply.

Li(s)+12Cl2(l)→LiCl(s) |

Li(s)+12Cl2(g)→LiCl(s) |

SO3(g)→12O2(g)+SO2(g) |

SO(g)+12O2(g)→SO2(g) |

2Li(s)+Cl2(g)→2LiCl(s) |

S(s)+O2(g)→SO2(g) |

The combustion of propane, C3H8, occurs via the reaction

C3H8(g)+5O2(g)→3CO2(g)+4H2O(g)

with heat of formation values given by the following table:

Substance |
ΔH∘f(kJ/mol) |

C3H8 (g) | -104.7 |

CO2(g) | −393.5 |

H2O(g) | −241.8 |

Calculate the enthalpy for the combustion of propane.

Answer #1

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The standard heat of formation, ΔH∘f, is defined as the
enthalpy change for the formation of one mole of substance from its
constituent elements in their standard states. Thus, elements in
their standard states have ΔH∘f=0. Heat of formation
values can be used to calculate the enthalpy change of any
reaction.
Consider, for example, the reaction
2NO(g)+O2(g)⇌2NO2(g)
with heat of formation values given by the following table:
Substance
ΔH∘f
(kJ/mol)
NO(g)
90.2
O2(g)
0
NO2(g)
33.2
Then the standard heat...

The standard heat of formation, ΔH∘f, is defined as the
enthalpy change for the formation of one mole of substance from its
constituent elements in their standard states. Thus, elements in
their standard states have ΔH∘f=0. Heat of formation
values can be used to calculate the enthalpy change of any
reaction.
Consider, for example, the reaction
2NO(g)+O2(g)⇌2NO2(g)
with heat of formation values given by the following table:
Substance
ΔH∘f
(kJ/mol)
NO(g)
90.2
O2(g)
0
NO2(g)
33.2
Then the standard heat...

The standard heat of formation, ΔH∘f, is defined as the enthalpy
change for the formation of one mole of substance from its
constituent elements in their standard states. Thus, elements in
their standard states have ΔH∘f=0. Heat of formation values can be
used to calculate the enthalpy change of any reaction.
Consider, for example, the reaction
2NO(g)+O2(g)⇌2NO2(g)
with heat of formation values given by the following table:
Substance ΔH∘f
(kJ/mol)
NO(g) 90.2
O2(g) 0
NO2(g) 33.2
Then the standard heat...

Part A
For which of the following reactions is ΔH∘rxn equal to
ΔH∘f of the product(s)?
You do not need to look up any values to answer this
question.
Check all that apply.
Hints
Check all that apply.
S(s)+O2(g)→SO2(g)
Li(s)+12F2(g)→LiF(s)
SO(g)+12O2(g)→SO2(g)
SO3(g)→12O2(g)+SO2(g)
2Li(s)+F2(g)→2LiF(s)
Li(s)+12F2(l)→LiF(s)
Part B
The combustion of propane, C3H8, occurs via the reaction
C3H8(g)+5O2(g)→3CO2(g)+4H2O(g)
with heat of formation values given by the following table:
Substance
ΔH∘f
(kJ/mol)
C3H8 (g)
-104.7
CO2(g)
−393.5
H2O(g)
−241.8
Calculate the enthalpy for...

Consider, for example, the reaction
2NO(g)+O2(g)⇌2NO2(g)
Then the standard heat of reaction for the overall reaction
is
ΔH∘rxn=ΔH∘f(products)−−ΔH∘f(reactants)
ΔH∘rxn=2(33.2)-[2(90.2)+0]= -114kJ
Part A
For which of the following reactions is ΔH∘rxn equal to
ΔH∘f of the product(s)?
You do not need to look up any values to answer this
question.
Check all that apply.
Na(s)+12Cl2(l)→NaCl(s)
2Na(s)+Cl2(g)→2NaCl(s)
Na(s)+12Cl2(g)→NaCl(s)
H2(g)+12O2(g)→H2O(g)
2H2(g)+O2(g)→2H2O(g)
H2O2(g)→12O2(g)+H2O(g)
Part B
The combustion of heptane, C7H16, occurs via the reaction
C7H16(g)+11O2(g)→7CO2(g)+8H2O(g)
with heat of formation values given by the following...

Calculate the enthalpy of the reaction 2NO(g)+O2(g)→2NO2(g)
given the following reactions and enthalpies of formation:
12N2(g)+O2(g)→NO2(g), ΔH∘A=33.2 kJ
12N2(g)+12O2(g)→NO(g), ΔH∘B=90.2 kJ

9. Use the following experimentally derived combustion
data to calculate the standard molar enthalpy of formation
(ΔH°f ) of liquid methanol (CH3OH) from its
elements.
2 CH3OH(l) + 3 O2(g) → 2
CO2(g) + 4 H2O(l)
ΔH°rxn = −1452.8 kJ
C(graphite) + O2(g) →
CO2(g)
ΔH°rxn = −393.5 kJ
2 H2(g) + O2(g) → 2
H2O(l)
ΔH°rxn = −571.6 kJ
(1) −238.7 kJ/mol (2) 487.7
kJ/mol (3) −548.3 kJ/mol
(4) 20.1 kJ/mol
(5) 47.1 kJ/mol

For which of the following reactions is ΔH∘rxn equal to
ΔH∘f of the product(s)?
You do not need to look up any values to answer this
question.
Check all that apply.
Hints
Check all that apply.
2Li(s)+F2(g)→2LiF(s)
S(s)+O2(g)→SO2(g)
SO3(g)→12O2(g)+SO2(g)
Li(s)+12F2(l)→LiF(s)
SO(g)+12O2(g)→SO2(g)
Li(s)+12F2(g)→LiF(s)

Constants | Periodic Table
Learning Goal:
To understand how standard enthalpy of reaction is related to
the standard heats of formation of the reactants and products.
The standard enthalpy of reaction is the enthalpy change that
occurs in a reaction when all the reactants and products are in
their standard states. The symbol for the standard enthalpy of
reaction is ΔH∘rxn, where the subscript "rxn" stands for
"reaction." The standard enthalpy of a reaction is calculated from
the standard heats...

Part A For which of the following reactions is ΔH∘rxn equal to
ΔH∘f of the product(s)? You do not need to look up any values to
answer this question. Check all that apply. Check all that apply.
1)Li(s)+12F2(l)→LiF(s)
.2) SO3(g)→12O2(g)+SO2(g).
3) SO(g)+12O2(g)→SO2(g)
. 4) 2Li(s)+F2(g)→2LiF(s).
5)S(s)+O2(g)→SO2(g)
.6) Li(s)+12F2(g)→LiF(s)

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