Bond Energies

Useful Concepts

Bond Energies

Bond energies can be very useful for providing estimates of the favourability of reactions by comparing the new bonds made in a reaction (exothermic) with the bonds broken during that reaction (endothermic).

Study Tip:
Remember that bond energies are the energy required to break a bond, that's an endothermic process .... it requires an energy INPUT.

The table shows some representative examples of some of the more common bonds.

		kJ/mol	kcal/mol
Homonulcear diatomics	H-H	435	104
	F-F	159	38
	Cl-Cl	242	58
	Br-Br	192	46
	I-I	150	36

H-X bonds	H-F	568	136
	H-Cl	431	103
	H-Br	366	87.5
	H-I	297	71
	H-OH	497	119
	CH₃O-H	426	102

C-H bonds	CH₃-H	435	104
	CH₃CH₂-H	410	98
	(CH₃)₂CH-H	397	95
	(CH₃)₃C-H	380	91
	C=C-H	450	108
	C≡C-H	535	128
	Ar-H	460	110
	C=CCH₂-H	368	88
	ArCH₂-H	355	85

C-C bonds	CH₃-CH₃	368	88
	CH₃CH₂-CH₃	355	85
	(CH₃)₂CH-CH₃	351	84
	(CH₃)₃C-CH₃	334	80

C-X bonds	CH₃-NH₂	364	87
	CH₃-OH	380	91
	CH₃-F	451	108
	CH₃-Cl	349	83.5
	CH₃-Br	293	70
	CH₃-I	234	56
Multiple bonds	C=C	611	146
	C≡C	837	200
	C=N	615	147
	C≡N	891	213
	C=O	749	179