Cambridge O Level Chemistry · Syllabus 5070 · Chemical Energetics
Bond Breaking
What is Bond Breaking?
The separation of bonded atoms, which requires an input of energy because it works against the attraction holding the atoms together; bond breaking is therefore an endothermic process.
This definition is part of the Chemical Energetics chapter in Cambridge O Level Chemistry.
Bond Breaking in context
Every chemical reaction both breaks bonds and makes bonds. Bond breaking is endothermic, because separating bonded atoms works against the attraction holding them together and needs an energy input; bond making is exothermic, because forming a bond releases energy. The overall enthalpy change is the balance: \(\Delta H\) equals the total energy taken in to break bonds minus the total energy given out when bonds form. If more energy is given out than taken in, the reaction is exothermic and \(\Delta H\) is negative; if less, it is endothermic and \(\Delta H\) is positive. Activation energy, \(E_\mathrm{a}\), is the minimum energy colliding particles must have to react.
Common mistakes with Bond Breaking
- 9. “Breaking a bond releases the energy that was stored in it.” Repair The single most damaging sentence in this topic. Bonded atoms attract each other; pulling them apart works against that attraction and therefore needs an energy input. Bond breaking is endothermic. Energy is released when bonds form.
Questions students ask about Bond Breaking
Does breaking a bond release energy?
No, and this is the single most damaging misconception in the topic. Bonded atoms attract one another, so pulling them apart works against that attraction and needs an energy input: bond breaking is endothermic. Energy is released when new bonds form: bond making is exothermic. Every reaction does both, and the sign of the overall enthalpy change depends only on which total is bigger, the energy taken in to break bonds or the energy given out when bonds are made.