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 standard heat of reaction for the overall reaction is

Δ*H*∘rxn===Δ*H*∘f(products)2(33.2)−114 kJ

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.

**Hints**

Check all that apply.

Na(s)+12Cl2(g)→NaCl(s) |

Na(s)+12Cl2(l)→NaCl(s) |

SO3(g)→12O2(g)+SO2(g) |

2Na(s)+Cl2(g)→2NaCl(s) |

SO(g)+12O2(g)→SO2(g) |

S(s)+O2(g)→SO2(g) |

Answer #1

ΔH^{∘}_{rxn} = ΔH^{∘}_{f}
[product(s)]

This will be true only when all the reactants used in given chemical reaction are in their native state.

This is the case with reactions

Na(s)+12Cl2(g)→NaCl(s)

2Na(s)+Cl2(g)→2NaCl(s)

S(s)+O_{2}(g)→SO_{2}(g)

Where, Na (s), Cl_{2} (g) S(s) & O_{2}(g)
both are in the so-called elemental state.

Note: Cl2(l) or Cl2 (s) state are not elemental states.

Hence Answe options : (1), (4), (6).

**=================XXXXXXXXXXXXXXXX=======================**

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 heat of...

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...

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...

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.
H2(g)+12O2(g)→H2O(g)
Na(s)+12Cl2(g)→NaCl(s)
2Na(s)+Cl2(g)→2NaCl(s)
H2O2(g)→12O2(g)+H2O(g)
Na(s)+12Cl2(l)→NaCl(s)
2H2(g)+O2(g)→2H2O(g)

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...

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

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.
Na(s)+12F2(g)→NaF(s)
SO(g)+12O2(g)→SO2(g)
Na(s)+12F2(l)→NaF(s)
2Na(s)+F2(g)→2NaF(s)
SO3(g)→12O2(g)+SO2(g)
S(s)+O2(g)→SO2(g)

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)

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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