Single Bond Energies Table

Thermochemistry Table

Metal tray with explosive thermite reaction occuring.
If the bond energies of the products are greater than that of the reactants, the chemical reaction will be exothermic. An example is the thermite reaction. Andy Crawford & Tim Ridley/Dorling Kindersley/Getty Images

Knowing the values for bond energy helps us to predict whether a reaction will be exothermic or endothermic.

For example, if the bonds in the product molecules are stronger than the bonds of the reactant molecules, then the products are more stable and have a lower energy than the reactants, and the reaction is exothermic. If the reverse is true, then energy (heat) must be absorbed in order for the reaction to occur, making the reaction endothermic. In this case, the products have a higher energy than the reactants. Bond energies may be used to calculate change in enthalpy, ΔH, for a reaction by applying Hess's Law. ΔH can be obtained from the bond energies only when all of the reactants and products are gasses.

Single Bond Energies (kJ/mol) at 25°C
H C N O S F Cl Br I
H 436 414 389 464 339 565 431 368 297
C 347 293 351 259 485 331 276 238
N 159 222 272 201 243
O 138 184 205 201 201
S 226 285 255 213
F 153 255 255
Cl 243 218 209
Br 193 180
I 151