Question 8.16: Use bond enthalpies from Table 8.6 to estimate the enthalpy ...

Use bond enthalpies from Table 8.6 to estimate the enthalpy of reaction for the combustion of methane:

CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)

Strategy Draw Lewis structures to determine what bonds are to be broken and what bonds are to be formed.

Setup

Bonds to break: 4 C—H and 2 O=O.
Bonds to form: 2 C=O and 4 H—O.
Bond enthalpies from Table 8.6: 414 kJ/mol (C—H), 498.7 kJ/mol (O=O), 799 kJ/mol (C=O in CO₂), and 460 kJ/mol (H—O).

TABLE 8.6	Bond Enthalpies
Bond	Bond Enthalpy (kJ/mol)	Bond	Bond Enthalpy (kJ/mol)
H-H*	436.4	N-N	193
H-N	393	N=N	418
H-O	460	N-N	941.4
H-S	368	N-O	176
H-P	326	N=O	607
H-F	568.2	N-F	272
H-Cl	431.9	N-Cl	200
H-Br	366.1	N-Br	243
H-I	298.3	N-I	159
C-H	414	O-O	142
C-C	347	O=O	498.7
C=C	620	O-P	502
C≡C	812	O=S	469
C-N	276	O-F	190
C=N	615	O-Cl	203
C≡N	891	O-Br	234
C-O	351	O-I	234
C=O†	745	P-P	197
C≡O	1070	P=P	489
C-P	263	S-S	268
C-S	255	S=S	352
C=S	477	F-F	156.9
C-F	453	Cl-Cl	242.7
C-Cl	339	Cl-F	193
C-Br	276	Br-Br	192.5
C-I	216	I-I	151
*Bond enthalpies shown in red are for diatomic molecules. †The C=O bond enthalpy in CO2 is 799 kJ/mol.

table 8.6

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