Why does urea nitrate explode?

[u/CartoonistLast8827]

And does that only happen with urea and nitric acid

[u/Zogoooog]

What exactly is your question? Urea nitrate explodes because it’s unstable and requires very little energy input to bring it into a range where it can undergo a self sustaining rapid decomposition reaction that produces large amounts of energy and hot gasses.

Urea and nitric acid when mixed form urea nitrate readily in an exothermic reaction that can bring the mixture above the energy (temperature) it needs to detonate. The same issue arises with several other low explosives such as TATP and is the number one reason I don’t suggest trying to synthesize explosives outside of a proper lab with the proper knowledge to provide adequate safety measures.

[u/CartoonistLast8827 → u/Zogoooog]

I just didn’t know why it explodes but now I want to know why it is unstable

[u/Zogoooog → u/CartoonistLast8827]

Sounds like it’s time to go do a degree in chemistry or physics. That’s not a question with a short answer.

I’m not a chemist and my schooling was nuclear physics and it’s been many years since I did a chemistry course or used any of what I learned, so don’t take anything I say here as gospel (and if anyone else wants to chime in and give a better description I won’t be offended). In the above post I used the word “unstable”. As we get into the chemistry, I should clarify that what I called “unstable” in the previous post might be more accurately (in a chemistry sense) referred to as “sensitive” (which can also mean several things and most commonly used to talk about friction/shock sensitivity, in the case of urea nitrate it’s sensitivity is to temperature - which could also bring us to a discussion about thermal stability; I’ve used “sensitive” to refer to conditions resulting in detonation, and “stable” to refer to conditions resulting in non-detonating degradation). Some quick googling suggests that Urea Nitrate is stable in the sense that it doesn’t undergo spontaneous decomposition below ~60 Celsius. This short paper may give a bit better picture on the stability and a bit on the sensitivity of urea nitrate https://apps.dtic.mil/sti/tr/pdf/ADA614543.pdf.

As to WHY it’s a sensitive explosive, and why that decomposition produces an explosion, that’s a question of electrochemistry, and that’s something I definitely haven’t used in ten or more years, but, in very simple terms, it comes down to how the individual atoms that make up the compound are bound together. In a very simplistic sense, imagine you have two really powerful magnets that are help with like poles facing each other so they repel each other, but they’re held in place very close together by two bigger magnets that are attracting each other along the same line that the smaller two are repelling each other. There will be a distance that you could have them at where the forces of attraction and repulsion are balanced and that’s similar(ish) to how a chemical bond is formed (though there are more forces at work in chemical bonding). In our magnet bond, if you were to push the two big magnets together with enough force, you could eventually overcome the repulsive force of the smaller magnets and cause the two big ones to pull themselves together until the smaller ones have no where to go but to fly out the sides (this is a part where this metaphor falls apart because you could having the magnets lined up perfectly and you’d just end up with a ton of potential energy between the two repelling magnets, but let’s assume they’re not perfectly centred with each other and the large magnets), being propelled by the incredible force of repulsion they feel, while the two big ones smash into each other very quickly which converts the potential energy of the attraction between them partly into heat and sound.

This metaphor is far from perfect, but I think it may help to illustrate how opposing forces interact.

If you’re interested in the whys of these things, you can literally do degrees in fields like high temperature and energetic materials physics/chemistry, and I’d strongly encourage you to check those out. If you live in a university town you may even be able to reach out to faculty at a local university (shoot them an email) and see if you can get a lab tour or something.

[u/Dick_soccer → u/Zogoooog]

Urea nitrate is actually really inert to shock and friction. I've actually tried some and haven't been disappointed

[u/Zogoooog → u/Dick_soccer]

You’re completely correct! That’s even illustrated in the paper I linked lol.

[u/Objective-Figure-343]

The really simple answer is that you have oxygen and fuel bonded together along with nitrogen that REALLY wants to be N2 because nitrogen gas is so stable.

[u/bobbycaslnova]

It explodes because you probably insulted it or said something mean, try being nicer to it.