Under normal atmospheric conditions, nitrogen (N₂) and oxygen (O₂) are stable, and the reaction between them does not occur easily. This is because nitrogen has a very strong triple bond between the two nitrogen atoms (N≡N), which requires a significant amount of energy to break. Similarly, oxygen (O₂) is a relatively stable diatomic molecule and does not react spontaneously with nitrogen at room temperature or pressure.
In order to initiate a reaction between N₂ and O₂, the molecules need to overcome the activation energy barrier, which is the energy required to break these strong bonds. Under normal conditions, the kinetic energy of nitrogen and oxygen molecules in the atmosphere is not sufficient to overcome this activation energy.
However, during a lightning strike, the situation changes drastically. Lightning is an electrical discharge that generates extremely high temperatures (around 3000°C) and a huge amount of energy in a very short amount of time. This immense energy provides the necessary activation energy to break the strong triple bond in nitrogen molecules (N≡N) and the double bond in oxygen molecules (O=O). This results in the formation of highly reactive atoms (nitrogen atoms and oxygen atoms), which can then combine to form nitrogen oxides (NO and NO₂), primarily nitric oxide (NO) in this case.
Once the lightning strike ends, the high temperature and energy dissipate, and the conditions are no longer conducive for the reaction to continue. Therefore, the reaction between nitrogen and oxygen only occurs during the brief duration of the lightning strike, after which the system cools and the reaction stops.