Question

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), Δ*H*∘A=33.2 kJ

12N2(g)+12O2(g)→NO(g), Δ*H*∘B=90.2 kJ

Answer #1

2NO(g)+O_{2}(g) → 2NO_{2}(g) ; H =
?
--------------------- (1)

Given reactions are

1/2N_{2}(g)+O_{2}(g) →
NO_{2}(g), ΔH^{∘}_{A}
=33.2
kJ
--------------------------(2)

1/2N_{2}(g)+1/2O_{2}(g) →
NO(g), ΔH^{∘}_{B} =90.2
kJ
-------------------------(3)

Eqn(1) can be obtained from Eqn(2) & Eqn(3) as follows :

Eqn(1) = [2x Eqn(1)] + [2xreverse of Eqn(2) ]

So H = (2x
ΔH^{∘}_{A} ] + [2x(-ΔH^{∘}_{B}
)]

= (2x33.2 kJ ) + [2x(-90.2 kJ)]

= -114.0 kJ

Therefore the enthalpy of the reaction is -114.0 kJ

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...

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...

Hess's law
states that "the heat released or absorbed in a chemical process is
the same whether the process takes place in one or in several
steps."
It is important to recall the following rules:
When two reactions are added, their enthalpy values are
added.
When a reaction is reversed, the sign of its enthalpy value
changes.
When the coefficients of a reaction are multiplied by a factor,
the enthalpy value is multiplied by that same factor.
Part A
Calculate...

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O2(g) + 2H2(g) → 2H2O (g) ΔH = − 483.7 kJ
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1.) Using enthalpies of formation, calculate the standard change
in enthalpy for the thermite reaction. The enthalpy of formation of
Fe3O4 is −1117 kJ/mol.
8 Al(s) + 3 Fe3O4(s) → 4 Al2O3(s) + 9 Fe(s)
2. a) Nitroglycerin is a powerful explosive, giving four
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