Cambridge O Level Chemistry · Syllabus 5070 · Chemical Energetics
Bond Making
What is Bond Making?
The formation of a chemical bond between atoms, which releases energy to the surroundings; bond making is therefore an exothermic process.
This definition is part of the Chemical Energetics chapter in Cambridge O Level Chemistry.
Bond Making 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.
Questions students ask about Bond Making
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.