1. Pure NH3 (Ammonia) does not burn in air:
* Reason: Ammonia is already a highly oxidized compound. It's difficult to further oxidize it in air to release more energy. In other words, there's not enough energy released in the reaction to sustain combustion.
2. Pure PH3 (Phosphine) is spontaneously flammable in air:
* Reason: Phosphine is much less stable than ammonia. It readily reacts with oxygen in the air, leading to a very exothermic reaction (a lot of heat is released) and the release of light (it burns).
3. Impurities in PH3 can impact flammability:
* While pure phosphine is flammable, the presence of impurities like diphosphine (P₂H₄) can actually make it *more* flammable. Diphosphine is even more reactive than phosphine and can trigger spontaneous combustion at lower concentrations.
Key Differences:
* Oxidation State: Ammonia has a higher oxidation state for nitrogen than phosphine has for phosphorus. This makes it harder to oxidize further.
* Bond Strength: The P-H bond in phosphine is weaker than the N-H bond in ammonia. This makes phosphine more prone to reacting with oxygen.
Important Note: While pure phosphine is flammable, it's not necessarily a good idea to experiment with it. Phosphine is highly toxic, and it's crucial to handle it with extreme care in well-ventilated areas.
Let me know if you have any other questions!
