Sciencemadness Discussion Board

Water production during combustion and its effect on heat ????

KonkreteRocketry - 2-5-2013 at 08:35

Ok so I have been trying to see into some insights of combustion performances of different Perchlorates

Actually, interestingly, in Ammonium perchlorate, half of the oxygen is not even usable and is turned into water. Or im not sure if the oxygen is burned with the H2. here is the ...

Ammonium perchlorate decomposition
2 NH4ClO4 = Cl2 + N2 + 2 O2 + 4 H2O

Ammonium perchlorate + Aluminum used in SRBs.
3 Al + 3 NH4ClO4 = Al2O3 + AlCl3 + 3 NO + 6H2O

So since here, is the H2O formed with exothermic reaction ? or simply formed from decomposition ? Because if it is not formed by exothermic reaction, then dosnt it mean in a SRB, the temperature will be dropped by the water since it has a high heat capacity and need a lot of heat to be heated up, so dosnt it mean less temperature in the SRB? so less Isp also ? So does this reaction

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

produce water with a exothermic reaction ? If its H2 burning with O then its very hot near 4000 degree, and if it dont burn it absorbs a lot of heat, since it needs so much energy to be heated up, and will have a big difference on my performance calculation for such combustion.

Also when KNO3 + Sugar is burned, H2O is also formed, but does it form from exothermic reaction ? from sources it burns only at 1400 degree so i'm 99% sure H2O is formed from decomposition of sucrose rather than the H actually being burned ? right i want a confirm on this also.

Thanks for reading, please answer me if you know this :)

DraconicAcid - 2-5-2013 at 10:30

I think you're making an artificial distinction. You want to look at the overall deltaH for the reaction that occurs; it does not matter what steps the reaction takes, or what you call those steps.

KonkreteRocketry - 2-5-2013 at 11:04

Quote: Originally posted by DraconicAcid  
I think you're making an artificial distinction. You want to look at the overall deltaH for the reaction that occurs; it does not matter what steps the reaction takes, or what you call those steps.


There are no delta H i cant find any info about it so ill do some basic calculations my self.

Trotsky - 4-5-2013 at 10:40

Don't forget that if you're going for blast damage all that water vapor will produce an incredible by-volume generation of gas. That's pretty useful

KonkreteRocketry - 4-5-2013 at 22:21

Quote: Originally posted by Trotsky  
Don't forget that if you're going for blast damage all that water vapor will produce an incredible by-volume generation of gas. That's pretty useful


good but do you know if those water are formed after H2 burning with O or it does not produce extra heat ?

KonkreteRocketry - 5-5-2013 at 08:02

3 Al + 3 NH4ClO4 = Al2O3 + AlCl3 + 3 NO + 6H2O

Cmon guys, does NO and H2O in above equation produce extra heat ? because it is formed when being burned, or is it just some molecular rearrangement ?

Some one please this curious question is killing me !

[Edited on 5-5-2013 by KonkreteRocketry]

plante1999 - 5-5-2013 at 08:07

What do you think? When you burn hydrogen, does it make energy? I mean common, it is easy to figure out.


KonkreteRocketry - 5-5-2013 at 08:12

Quote: Originally posted by plante1999  
What do you think? When you burn hydrogen, does it make energy? I mean common, it is easy to figure out.



but it forms within itself since decomposition

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

here ? it was only heated.

plante1999 - 5-5-2013 at 08:16

If you put a charge with ammonium perchlorate around it, it can detonate, making water. It is a good sign the molecule chemical energy is easily turned to mechanical/thermal energy.

KonkreteRocketry - 5-5-2013 at 08:20

Quote: Originally posted by plante1999  
If you put a charge with ammonium perchlorate around it, it can detonate, making water. It is a good sign the molecule chemical energy is easily turned to mechanical/thermal energy.


how come... but i asked another chemist on facebook he said this reaction does not make extra heat on the formation of H2O

Ral123 - 5-5-2013 at 10:23

Where's your critical thinking people?? Formation of H2O from H2 and 1/2 O2 gives 241.818kj per mole. Hydrogen atoms are a dream fuel for rockets and explosives. It gives great energy per weight, and it gives superb expansion of gases. Unlike carbon fuel, it doesn't shift it's equilibrium to energetically less desirable configuration CO2+C<->2CO. The ultimate price however is the lack of density.

KonkreteRocketry - 5-5-2013 at 12:00

Quote: Originally posted by Ral123  
Where's your critical thinking people?? Formation of H2O from H2 and 1/2 O2 gives 241.818kj per mole. Hydrogen atoms are a dream fuel for rockets and explosives. It gives great energy per weight, and it gives superb expansion of gases. Unlike carbon fuel, it doesn't shift it's equilibrium to energetically less desirable configuration CO2+C<->2CO. The ultimate price however is the lack of density.


but since the water formed from decomposition instead of combustion, dosnt that mean this water, is not formed from burning H2 with O ?

I can decompose sugar to get water too.

Trotsky - 5-5-2013 at 12:13

Is there a difference? The atoms popping apart and recombining release energy. The difference is the pace of reaction, is it not?

Ral123 - 5-5-2013 at 12:36

Quote: Originally posted by KonkreteRocketry  
Quote: Originally posted by Ral123  
Where's your critical thinking people?? Formation of H2O from H2 and 1/2 O2 gives 241.818kj per mole. Hydrogen atoms are a dream fuel for rockets and explosives. It gives great energy per weight, and it gives superb expansion of gases. Unlike carbon fuel, it doesn't shift it's equilibrium to energetically less desirable configuration CO2+C<->2CO. The ultimate price however is the lack of density.


but since the water formed from decomposition instead of combustion, dosnt that mean this water, is not formed from burning H2 with O ?

I can decompose sugar to get water too.

If I burn ammonia in perchloric acid, you suggest I'll get as much energy as heating sugar? People like you should orient towards commercial products. They don't require critical thinking. Or at least established recipes.

KonkreteRocketry - 6-5-2013 at 00:26

Quote: Originally posted by Ral123  
Quote: Originally posted by KonkreteRocketry  
Quote: Originally posted by Ral123  
Where's your critical thinking people?? Formation of H2O from H2 and 1/2 O2 gives 241.818kj per mole. Hydrogen atoms are a dream fuel for rockets and explosives. It gives great energy per weight, and it gives superb expansion of gases. Unlike carbon fuel, it doesn't shift it's equilibrium to energetically less desirable configuration CO2+C<->2CO. The ultimate price however is the lack of density.


but since the water formed from decomposition instead of combustion, dosnt that mean this water, is not formed from burning H2 with O ?

I can decompose sugar to get water too.

If I burn ammonia in perchloric acid, you suggest I'll get as much energy as heating sugar? People like you should orient towards commercial products. They don't require critical thinking. Or at least established recipes.


H2O probably came from molecular rearrangement during Thermal decomposition of NH4ClO4.

Sucrose does not have any H2O already bonded together either,

http://www.elmhurst.edu/~chm/vchembook/images/543chairglucos...

The H have to find the other H and O, and during sucrose's thermal decomposition, the H2O forming does not give extra heat, so why should NH4ClO4 give extra heat ? some one explain ? It is probably the H ions are too reactive to stay alone which is why it has to get the O, without combustion.

simply RED - 6-5-2013 at 04:51

Come on, to establish the energy output you need to subtract the energy of the final products and reagents. It is as simple as thermodynamics :) .

KonkreteRocketry - 6-5-2013 at 07:04

Also i think it does not make sense if H2 and O was released for them to combust to form H2O during a decomposition process, because Cl gas is also present, why doesnt HCl form but H2O form ?

Ral123 - 6-5-2013 at 09:08

Cl2 and O2 are existing in equilibrium and are "fighting" for the hydrogen. OK?

DraconicAcid - 6-5-2013 at 09:21

Here: http://www.kentchemistry.com/links/Kinetics/BondEnergy.htm

Antiswat - 6-5-2013 at 09:30

i think whats being wondered about here to put it down with other words, does the formed H2O from this reaction go into hydrogen and oxygen and then again react (:
or does it lower the overall temperature and not decompose into hydrogen and oxygen which then reacts

Trotsky - 6-5-2013 at 12:48

In detonation are not all bonds (more or less) breaking apart then recombining?

They aren't just magically producing the byproducts. There isn't some sort of quantum rearrangement. I admit that I don't have the best understanding but the energy produced from 2H and O coming together to make water should be the same regardless of whether you're burning them or they're coming together in detonation. I mean, and it's been said before, the only real difference is the pace of the reaction.

Actually, and to me it's a more interesting question, do the products of, say, nitrocellulose detonating differ from those of nitrocellulose deflagration or (if possible) nitrocellulose simply burning?

I assume that the temperature would have a greater impact, certainly pressure, which would raise the temp would have a major impact. Some compounds show an enormous increase in burn rate when pressurized. R-Candy is a good example. A two pound motor would take as long as ten minutes to burn in the open air (and fog out every mosquito for three square miles!) But you put that in a properly built motor and it'll burn out in seconds.

Ral123 - 6-5-2013 at 21:21

Everything with out perfect OB gives different products at different conditions. According to the russain wiki, TNP gives most energy when detonated at maximum density:
C6H3O(NO2)3->1.5H2O+2.75CO2+3.25C
Separate and combine H2 and O2 as much as you wants. The final product will effect how much energy you've gained.

KonkreteRocketry - 7-5-2013 at 09:48

well its not about separating H2 and O2 ho many times.. well..

Here does NH4 act as an iconic bond for ClO4 in NH4ClO4 ? if so

Does it takes energy to separate NH4 from ClO4 for further decomposition ?

how much energy does Li need to separate it self from LiClO4 ? I have not learned how to calculate heat with ionic bonds yet, and how much heat does LiCl gains when Li forms an ionic bond with Cl ?

Ral123 - 7-5-2013 at 13:13

LiClO4->LiCl+1.5O2 doesn't yield or take much energy. You can then calculate with the elemental O2.

KonkreteRocketry - 7-5-2013 at 14:46

Ok cool,

I cant find any enthalpy of Cl = O bonds, so then i found Chlorine dioxide on wikipedia which is O=Cl=O says the enthalpy is 104.60, so can i assume Cl = O is half of 104.60 ?

[Edited on 7-5-2013 by KonkreteRocketry]

[Edited on 7-5-2013 by KonkreteRocketry]

DraconicAcid - 7-5-2013 at 14:50

Quote: Originally posted by KonkreteRocketry  
Ok cool,

I cant find any enthalpy of Cl = O bonds, so then i found Chlorine dioxide on wikipedia which is O=Cl=O says the enthalpy is 104.60, so can i assume Cl = O is half of 104.60 ?

No, that's the enthalpy of formation, not a bond enthalpy.

KonkreteRocketry - 7-5-2013 at 15:14

Quote: Originally posted by DraconicAcid  
Quote: Originally posted by KonkreteRocketry  
Ok cool,

I cant find any enthalpy of Cl = O bonds, so then i found Chlorine dioxide on wikipedia which is O=Cl=O says the enthalpy is 104.60, so can i assume Cl = O is half of 104.60 ?

No, that's the enthalpy of formation, not a bond enthalpy.


but if i know they got the enthalpy from Cl2 + O2 i can still work out the C=O energy right ?

DraconicAcid - 7-5-2013 at 15:21

Quote: Originally posted by KonkreteRocketry  
Quote: Originally posted by DraconicAcid  
Quote: Originally posted by KonkreteRocketry  
Ok cool,

I cant find any enthalpy of Cl = O bonds, so then i found Chlorine dioxide on wikipedia which is O=Cl=O says the enthalpy is 104.60, so can i assume Cl = O is half of 104.60 ?

No, that's the enthalpy of formation, not a bond enthalpy.


but if i know they got the enthalpy from Cl2 + O2 i can still work out the C=O energy right ?

You can work it out. Show your calculations, and I'll tell you if you're on the right track.

Ral123 - 7-5-2013 at 21:39

Don't work it out. Use wikipedia, youtube and people's opinion about propellant performance.

Dornier 335A - 10-5-2013 at 12:38

You don't have to care about the enthalpy of single bonds inside the molecule. The enthalpy of formation is easy to find for many compounds.
Neither is all the steps in the reaction relevant. All you have to know is the reactants' ΔHf and the products' ΔHf.
The enthalpy change of reaction is the sum of ΔH for the products minus the sum of ΔH for the reactant(s).

The decomposition of NH4ClO4
2 NH4ClO4(s) → Cl2(g) + N2(g) + 2 O2(g) + 4 H2O(g)
(1*0 + 1*0 + 2*0 + 4*-241.8)-(2*-295.3)

The ΔH of this reaction is -380.6 kJ/mol so it is exothermic. And yes, it is the water produced in the reaction that liberates this energy.