Nitrogen's Big Journey
Trace nitrogen from air to soil to plants.
What this lesson covers
Why it matters
Lightning strikes the sky, turning inert air into a chemical fuel for life. This violent spark is nature's way of fixing nitrogen.
The idea in plain words
Balance check: confirm that one molecule of N₂ and one of O₂ yield two molecules of NO.
Predict first
Why doesn't nitrogen react with oxygen under normal conditions?
Nitrogen gas has a triple bond that requires massive energy to break, which is why we need lightning or high heat.
- Nitrogen is too heavy to move
- The triple bond in N₂ is very strong and stable — correct
- Nitrogen is a noble gas
- Oxygen repels nitrogen
What you do
Trace nitrogen through the sky: lightning forces N₂ + O₂ → 2NO, the cooling air turns it 2NO + O₂ → 2NO₂, then rain washes it down as 4NO₂ + 2H₂O + O₂ → 4HNO₃ — nitrates that feed the soil.
Check yourself
What is the product of the reaction between nitrogen and oxygen in lightning?
The direct combination at high temperature produces nitric oxide: N₂ + O₂ → 2NO.
Why is this reaction important for plants?
This is the first step of natural nitrogen fixation, making atmospheric nitrogen available for biological use.
What condition is required for this reaction to occur?
The strong triple bond in N₂ requires high energy input, such as the heat from lightning, to break.
- Nitrogen dioxide (NO₂)
- Nitric oxide (NO) — correct
- Ammonia (NH₃)
- It provides oxygen for respiration
- It converts inert N₂ into a form that can eventually become nitrates — correct
- It cools the soil down
- Low temperature and pressure
- Very high temperature (like lightning) — correct
- Presence of water only