Given the bond-dissociation energies: nitrogen-to-oxygen bond in N O , 631 k J m o l − 1 , H − H in H 2 , 436 k J m o l 1 ; N − H in H 2 O , 463 k J m o l − 1 ; N − H calculate Δ r H for the reaction below. 2 N O ( g ) + 5 H 2 ( g ) → 2 N H 3 ( g ) + 2 H 2 O ( g )
Given the bond-dissociation energies: nitrogen-to-oxygen bond in N O , 631 k J m o l − 1 , H − H in H 2 , 436 k J m o l 1 ; N − H in H 2 O , 463 k J m o l − 1 ; N − H calculate Δ r H for the reaction below. 2 N O ( g ) + 5 H 2 ( g ) → 2 N H 3 ( g ) + 2 H 2 O ( g )
Solution Summary: The author explains how the Delta_rH of the given reaction should be determined.
Given the bond-dissociation energies: nitrogen-to-oxygen bond in
N
O
,
631
k
J
m
o
l
−
1
,
H
−
H
in
H
2
,
436
k
J
m
o
l
1
;
N
−
H
in
H
2
O
,
463
k
J
m
o
l
−
1
;
N
−
H
calculate
Δ
r
H
for the reaction below.
2
N
O
(
g
)
+
5
H
2
(
g
)
→
2
N
H
3
(
g
)
+
2
H
2
O
(
g
)
Formula Formula Bond dissociation energy (BDE) is the energy required to break a bond, making it an endothermic process. BDE is calculated for a particular bond and therefore consists of fragments such as radicals since it undergoes homolytic bond cleavage. For the homolysis of a X-Y molecule, the energy of bond dissociation is calculated as the difference in the total enthalpy of formation for the reactants and products. X-Y → X + Y BDE = Δ H f X + Δ H f Y – Δ H f X-Y where, ΔHf is the heat of formation.
For each reaction, identify another quantity that is equal to AHn.
CH,(g) + 20,(g) → CO,(g) + 2 H,0(1)
CH,(g) → C(g) + 4 H(g)
O enthalpy of formation of CO, (g)
-4 x bond energy of C-H
4 x bond energy of C-H
enthalpy of formation of C(g)
O enthalpy of combustion of CH
4 x bond energy of C–H
O -4 x bond energy of C–H
O enthalpy of combustion of CH,
C (graphite) + 2 H,(g)
→ CH,(g)
C(g) + 4 H(g) → CH,(g)
O 4x bond energy of C-H
O -4 x bond energy of C-H
enthalpy of combustion of C
O -4 x bond energy of C-H
O enthalpy of formation of CH,(g)
O enthalpy of formation of CH,(g)
enthalpy of combustion of CH,
4 x bond energy of C-H
Predict the enthalpy of reaction from the average bond enthalpies for the following reaction: 2C2H6(g) + 7O2(g)
→
4CO2(g) + 6H2O(g)
Bond
Enthalpy (kJ/mol)
H―H
436.4
H―O
460
C―H
414
C―C
347
C═C
620
C―O
351
O―O
142
O═O
498.7
C═O
745
C═O(in carbondioxide)
799
______ kJ
For the reaction:
2C₂H6(g) + 70₂(g) 4CO₂(g) + 6H₂O(g)
Part 1 of 2
Predict the enthalpy of reaction from the average bond enthalpies. Be sure your answer has the correct number of significant digits.
Note: Reference the Bond energies table for additional information.
ΔΗ
rxn
Part 2 of 2
-
kJ
mol
Calculate the enthalpy of reaction from the standard enthalpies of formation of the reactant and product molecules. Be sure your answer has
the correct number of significant digits.
Note: Reference the Thermodynamic properties of pure substances table for additional information.
AH =
rxn
kJ
mol
0XP
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The Laws of Thermodynamics, Entropy, and Gibbs Free Energy; Author: Professor Dave Explains;https://www.youtube.com/watch?v=8N1BxHgsoOw;License: Standard YouTube License, CC-BY