Question

From the enthalpies of reaction 2H2(g)+O2(g)→2H2O(g)ΔH=−483.6kJ3O2(g)→2O3(g)ΔH=+284.6kJ calculate the heat of the reaction 3H2(g)+O3(g)→3H2O(g) Express your answer using four significant figures. I have no idea how to approach this problem.

Answer #1

2H2(g)+O2(g)→2H2O(g)
ΔH_{1}=−483.6kJ .....(1)

3O2(g)→2O3(g)
ΔH_{2}=+284.6kJ ......(2)

calculate the heat of the reaction

3H2(g)+O3(g)→3H2O(g)
ΔH_{3}= ? ..................(3)

So we have to calcualte enthalpy of reaction (3) from given enthalpies of reaction (1) and (2)

We will combine the two equations so that we can obtain the third equaiton

Equation (3) = 1.5 X (equation (1)) - (0.5 X Equation (2))

Enthalpy ((3) = 1.5 X enthalpy of (1) - 0.5 X enthalpy of (2)

ΔH_{3}= 1.5 X (−483.6kJ) - (0.5 X +284.6kJ) = -725.4 -
142.3 = -867.7 kJ

Applying Hess’s Law, from the enthalpies of reactions,
N2(g) + 3H2(g) → 2 NH3(g) ΔH = − 91.8 kJ
O2(g) + 2H2(g) → 2H2O (g) ΔH = − 483.7 kJ
N2(g) + O2(g) → 2NO(g) ΔH = 180.6 kJ
Calculate the enthalpy change (ΔHrxn) for the reaction: 4NH3(g)
+ 5O2(g) → 4 NO (g) + 6H2O(g)

Problem 5.64 Part A From the enthalpies of reaction
2C(s)+O2(g)→2CO(g)ΔH=−221.0kJ
2C(s)+O2(g)+4H2(g)→2CH3OH(g)ΔH=−402.4kJ calculate ΔH for the
reaction CO(g)+2H2(g)→CH3OH(g)

Calculate the ΔH∘ for this reaction using the following
thermochemical data:
CH4(g)+2O2(g)⟶CO2(g)+2H2O(l)
ΔH∘=−890.3kJ
C2H4(g)+H2(g)⟶C2H6(g)
ΔH∘=−136.3kJ
2H2(g)+O2(g)⟶2H2O(l)
ΔH∘=−571.6kJ
2C2H6(g)+7O2(g)⟶4CO2(g)+6H2O(l)

Calculate ΔH∘rxn. C2H5OH(l)+3O2(g)→2CO2(g)+3H2O(g) Express your
answer using five significant figures.

Consider the following chemical reaction: 2H2O(l)→2H2(g)+O2(g)
What mass of H2O is required to form 1.5 L of O2 at a temperature
of 325 K and a pressure of 0.946 atm ? Express your answer using
two significant figures.

From the enthalpies of reaction
H2(g)+F2(g)→2HF(g)ΔH=−537kJ
C(s)+2F2(g)→CF4(g)ΔH=−680kJ
2C(s)+2H2(g)→C2H4(g)ΔH=+52.3kJ
Calculate ΔH for the reaction of
ethylene with F2: C2H4(g)+6F2(g)→2CF4(g)+4HF(g)

What mass of natural gas (CH4) must you burn to emit 275 kJ of
heat?
CH4(g)+2O2(g)→CO2(g)+2H2O(g)ΔH∘rxn=−802.3kJ
m =
Pentane (C5H12) is a component of gasoline that burns according
to the following balanced equation:
C5H12(l)+8O2(g)→5CO2(g)+6H2O(g)
Part A
Calculate ΔH∘rxn for this reaction using standard
enthalpies of formation. (The standard enthalpy of formation of
liquid pentane is -146.8 kJ/mol.)
Express your answer using five significant figures.
ΔH∘rxn =
kJ

Nitromethane (CH3NO2) burns in air to produce significant
amounts of heat.
2CH3NO2(l)+(3/2)O2(g)→ 2CO2(g)+3H2O(g)+N2(g)
ΔH∘rxn=−1418kJ
How much heat is produced by the complete reaction of 5.02 kg of
nitromethane?
Express your answer with the appropriate units.
q = ??

We can use Hess's law to calculate enthalpy changes that cannot
be measured. One such reaction is the conversion of methane to
ethylene:
2CH4(g)⟶C2H4(g)+2H2(g)
Part A
Calculate the ΔH∘ for this reaction using the following
thermochemical data:
CH4(g)+2O2(g)⟶CO2(g)+2H2O(l)
ΔH∘=−890.3kJ
C2H4(g)+H2(g)⟶C2H6(g)
ΔH∘=−136.3kJ
2H2(g)+O2(g)⟶2H2O(l)
ΔH∘=−571.6kJ
2C2H6(g)+7O2(g)⟶4CO2(g)+6H2O(l)
ΔH∘=−3120.8kJ
Express your answer to four significant figures and include the
appropriate units.

Consider the following reaction:
2NO(g)+2H2(g)→N2(g)+2H2O(g).
If the rate constant for this reaction at 1000 K is
6.0×104M−2s−1, what is the reaction rate when [NO]=
2.90×10−2M and [H2]=
1.80×10−2M?
Express your answer using two significant figures.
rate =
M/s
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Part C
What is the reaction rate at 1000 K when the concentration of NO
is increased to 0.14 M, while the concentration of H2 is
1.80×10−2M?
Express your answer using two significant figures.

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