When bonds are formed, does the bond energy increase? When they break, does the bond energy decrease?
The bond energy is defined as equal to the amount of energy given out when the bond is made (or absorbed when that the bond is broken).
So when a bond is made, and the system cools to its original energy, the amount of energy given out, -DeltaH, is more or less equal to the bond energy.
Noticed that minus sign. For a process that releases heat, DeltaH is negative.
When bonds break, energy has to be supplied. When bonds form, energy is released. If the total energy released from forming bonds is higher than the total energy absorbed from breaking bonds, the reaction is exothermic; if it is the other way around, the reaction is endothermic.
A specific bond will always have a specific energy; bond energy does not change. It can be affected by the chemical surroundings, but in a specific setting, it is constant.
References :
The bond energy is defined as equal to the amount of energy given out when the bond is made (or absorbed when that the bond is broken).
So when a bond is made, and the system cools to its original energy, the amount of energy given out, -DeltaH, is more or less equal to the bond energy.
Noticed that minus sign. For a process that releases heat, DeltaH is negative.
References :