NH4ClO4 Decomposition question.

[DubaiAmateurRocketry]

When ammonium perchlorate decompose, half of its oxygen end up becoming water, umm interesting,

2 NH4ClO4 + HEAT = Cl2 + N2 + 2 O2 + 4 H2O

 

so is the water formed from molecular rearrangement or combustion of H2 + O ? so basically does the H2O give extra heat ?

[Mumbles]

Thermodynamically there is no difference between direct formation or the generation of free oxygen and hydrogen, and subsequent combustion. Enthalpy is a state function, so it only matters where you start and where you end, not the path you take to get there.

[DubaiAmateurRocketry]

Thermodynamically there is no difference between direct formation or the generation of free oxygen and hydrogen, and subsequent combustion. Enthalpy is a state function, so it only matters where you start and where you end, not the path you take to get there.

 

how does that make sense ? i can decompose sugar as well to get H2O, but that does not give me extra heat ?

[Mumbles]

I can't explain the entirety of thermodynamics to you. If you really want to understand it, you're going to need to do some serious reading.

 

Energies all all relative, and can be thought of in many different ways. For me, the one that makes the most sense is gravitational potential energy. The higher you raise an object, the more potential energy you give it. If you take a ball from ground level, and bring it up to 50 meters it has the same potential energy no matter how you got it there. Taking the elevator or stairs has no impact on the potential energy imparted to the ball, even though the different paths to get there are going to be different, and could be more or less difficult.

 

Enthalpy works the exact same way. It only matter what you start from, and what you end with. What happens in between has no impact what-so-ever on the total energy gained or lost. To use your example going from AP to water directly via molecular rearrangement has some amount of energy change associated with it. If you instead form molecular hydrogen and molecular oxygen from AP, and then combust that, it would have the same overall energy change. Yes, combusting hydrogen with oxygen does give off energy. However there is also going to be an energy cost associated with forming the molecular hydrogen and oxygen. The energy cost of formation combined with the energy gain of combustion equal out to form the exact same energy change associated with a molecular rearrangement.

 

If you want to know more, I suggest picking up a physical chemistry book and start reading.

[DubaiAmateurRocketry]

I can't explain the entirety of thermodynamics to you. If you really want to understand it, you're going to need to do some serious reading.

 

Energies all all relative, and can be thought of in many different ways. For me, the one that makes the most sense is gravitational potential energy. The higher you raise an object, the more potential energy you give it. If you take a ball from ground level, and bring it up to 50 meters it has the same potential energy no matter how you got it there. Taking the elevator or stairs has no impact on the potential energy imparted to the ball, even though the different paths to get there are going to be different, and could be more or less difficult.

 

Enthalpy works the exact same way. It only matter what you start from, and what you end with. What happens in between has no impact what-so-ever on the total energy gained or lost. To use your example going from AP to water directly via molecular rearrangement has some amount of energy change associated with it. If you instead form molecular hydrogen and molecular oxygen from AP, and then combust that, it would have the same overall energy change. Yes, combusting hydrogen with oxygen does give off energy. However there is also going to be an energy cost associated with forming the molecular hydrogen and oxygen. The energy cost of formation combined with the energy gain of combustion equal out to form the exact same energy change associated with a molecular rearrangement.

 

If you want to know more, I suggest picking up a physical chemistry book and start reading.

 

I so, formation of CO2 gives heat, formation of CaO gives heat.

 

and i can make both of them from heating CaCO3, which does not give heat at all. Please explain a bit more..

 

Why should NH4ClO4 's formation of water give heat, and why Sucrose's for example, dont. I studied chemistry my own so i really skipped a lot. thx.

[Mumbles]

The change in heat is actually a simple equation. Heat is energy. Remember this for it to make sense.

 

The change in energy = (total energy in all bonds of products) - (total energy in all bonds of reactants)

 

If the products contain more energy than the reactants, it requires an energy input and thus is endothermic. If the reactants contain more energy, there is surplus energy which is released as heat, light, and other forms of energy. This is exothermic.

 

Like I said before, it only matters where you start and where you finish. Starting from AP to water is a downhill process. Starting from sucrose to water, is an uphill process. It sounds like you skipped way too much. If you want to try to understand this stuff, you might need to revisit these things.

[GalFisk]

To take the CaCO3 example:

Formation of CaO and CO2 from constituent elements gives heat. If you split your carbonate into calcium, oxygen and carbon, you'll use a certain amount of energy. If you then react the oxygen with calcium and carbon to get CaO and CO2, you will get some, but not all, of the energy back. You can say that CaCO3 has the lowest energy level, separate elements have the highest, and CO2+CaO is intermediate.

When you split CaCO3 directly into CaO+CO2, you're going from the low to the intermediate enegy level, without passing through the high level, so you'll have a purely endothermic reaction.