Question

**Part A**

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.

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 the combustion of 1 mole of propane.

Express your answer to four significant figures and include the appropriate units.

Answer #1

Part A: enthalpy of reactions = formation enthalpy of products - formation enthalpy of reactants

criteria: enthalpy of formation of any element (solid, liquid, gas state) is zero

so, enthalpy of reactions = formation enthalpy of products for following reactions

S(s)+O2(g)→SO2(g) |

Li(s)+12F2(g)→LiF(s) |

2Li(s)+F2(g)→2LiF(s) |

Li(s)+12F2(l)→LiF(s) |

Part B:

enthalpy of combustion = formation enthalpy of products - formation enthalpy of reactants

= [3*(−393.5) + 4*(−241.8) - (-104.7 + 0) ] kj/mole

= - 2043 kj/mole

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)

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)

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.
CO(g)+12O2(g)→CO2(g)
BaCO3(s)→BaO(s)+CO2(g)
Li(s)+12F2(l)→LiF(s)
Li(s)+12F2(g)→LiF(s)
2Li(s)+F2(g)→2LiF(s)
C(s,graphite)+O2(g)→CO2(g)

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...

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)

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...

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)

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...

Use data from Appendix IIB to calculate ?S?rxn in J/K
for each of the reactions given below.
A.
3NO2(g)+H2O(l)?2HNO3(aq)+NO(g)
B. Cr2O3(s)+3CO(g)?2Cr(s)+3CO2(g)
C.
SO2(g)+12O2(g)?SO3(g)
D
.N2O4(g)+4H2(g)?N2(g)+4H2O(g)

Liquefied petroleum (LP) gas burns according to the following
exothermic reaction:
C3H8(g)+5O2(g)→3CO2(g)+4H2O(g)ΔH∘rxn=−2044kJ
.
Part A
What mass of LP gas is necessary to heat 1.8 L of water from
room temperature (25.0 ∘C) to boiling (100.0 ∘C)? Assume that,
during heating, 14% of the heat emitted by the LP gas combustion
goes to heat the water. The rest is lost as heat to the
surroundings.
Express your answer using two significant figures.

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