Mix of NH3 and H2

I got a C in chemistry so don't bank on my answer.

NH₃ is a pretty stable molecule, N has 5 valence electrons and H have one each so the N attracts 3 H to make it a stable 8 valence. H₂ is stable because both have one valence electron and share to fill each others shells.

I do not think there will be any molecular reaction by mixing the two. They will mix homogeneously though due to....some law who's name escapes me.

If you chilled the container, at the condensation point the one with the warmer phase change point will start precipitating out (raining). Volume of the container would begin decreasing as soon as the temp begins to lower. When condensation occurs the volume will decrease more until the temp is low enough that both have condensed out and all you are left with is a mixture of liquids or one may freeze and you will have a solid and liquid. The liquids will have similar chemical properties and will not undergo a molecular change.

You are going to have to google the phase change temps for each if you want to know (or someone else will tell you) I am too tired tonight to look it up for you.

I hope this explains your scenario. The Air Force taught me that at 1 atmosphere pressure, one gallon of liquid oxygen or was it nitrogen(?) well one of them makes about 600 square feet of gas. I could look through my notes to find the exact calculations that will tell you if you need to know.

Drew

Not a chemist but I think:

2NH3 + H2 <--->2NH4+ a reversible reaction (no chemicals have left the reaction)

You may lose some H2 to create ammonium ion in the reaction if ratio of NH3:H2 is low. ??

This is incorrect. Ions are not formed in the vapour phase at ambient temperature.

Thanks PW, I knew it was just too simple.

Reminds me of the time a chemist, a physicist, and a biologist visited the ocean for the first time:

The physicist seeing the water and thinking of the particles and bonds of all the water and salt and dove into the ocean and did not return,

The biologist seeing all the water and thinking of all the life in the ocean dove into it and never returned.

The chemist mulled over what had just happened and applying his observation skills deduced that physicists and biologist are soluble in salt water.

two gasses mix and make no compounds as long as they are warm and each component acts like an ideal gas. H2 is more ideal, as it condenses at a very low temp, much lower than NH3. If you get close the the condensation point of the NH3 you might have some azeotropism around the condensation point of the NH3.

here are some links you can drill into, some people have explored this binary systems.

http://www.google.ca/#hl=en&safe=off&q=H2+%2BNH3+%2Bbinary&meta=&aq=f&aqi=&aql=&oq=H2+%2BNH3+%2Bbinary&gs_rfai=&fp=7bdd19b300c6b795

I tried the links but they want you to pay for deeper information. and i have not found the meaning of the word, "azeotropism" what is it?

So the gasses will remain seperate, and if the gasses were to cool below the -35 or so the NH3 sould condence out?

Thanks

they will not remain separate, they will be intimately mixed. Some want $$, just drill down further, you might find 2-3 useful links per page and there are many of them.

These search leeches are avoidable.

Once you get below the condensation point of the partial pressure of NH3, it will condense. It might also form an azeotrope with H2? you will have to drill.

what is the purpose of this mixture? Nh3 can be used as a lifting gas, safer than H2, but less lift, cheaper then He

with an atomic weight of 17 compared to air at about 28.6 it is better than hot air, but it smells bad and is toxic. Adding H2 gives lift, but adds combustibility. H2 has a wide explosive range, so a little air makes it bangable.

http://en.wikipedia.org/wiki/Azeotrope

Yes it has nh3 about 1/8the the lifting power of H2

But I was thinking in our balloon missions about trying it some either at 100% or a blend. where say 90% of the lift is provided by H2 and the remainder and some to provide the lift to make it positive boyuant and rise into the atmosphere.

But as it gets higher it of course gets colder and it easily gets colder than the boiling point of the NH3 and it starts to condense out, and the balloon looses it's lift. nd either becomes neutral bouyant, or if it condenced too far it starts to sink and of course it then gets warmer and the NH3 boils offagain and regains its lifting eventually it floats in a narrow altitude.

or at least a possible plan/

Joe

I think no reaction will occur and as far as the two gases were trapped in one contianer they will mix and collagative properties may occur and the physical properties of both gases (bioling point, freeze point etc) will be affected and make new physical propeerties of the mixure. So to think about properties of NH3 alone to affect floating of balloon in variable alltitutes I think it is not correct.

There is no chemical reaction between NH₃ and H₂. They simply form a mixture.

This is a great answer. My thoughts and questions are mixed in below.

In a balloon, the 2 gases will mix and they will each have a partial pressure of 1/2 an atmosphere.

Ok for calculating purposes lets go with the 1/2 atm level. IE: 18,000 feet, typical temp art that level isn't cold enough yet tho, but say it is, average there is, -20C

Cooling to -33C will not condense the NH3 because it's pressure will be 1/2 an atmosphere.

ok This morning the temp aloft got to, -33C at, roughly 8000 meters elevation, which would be 0.351343 Atmospheres. Quite a bit lower than sea level pressure.

Here is the complete sounding profile for you all to examine. Hopefully the cloumns wont get too messed up, Ok they do get messed up some, the third colum is the temp in degrees C i made the first two rows in bold font to show the temp colum, just take it on down.

72645 GRB Green Bay Observations at 12Z 06 Apr 2010

-----------------------------------------------------------------------------
PRES HGHT TEMP DWPT RELH MIXR DRCT SKNT THTA THTE THTV
hPa m C C % g/kg deg knot K K K
-----------------------------------------------------------------------------
1000.0 65
983.0 214 9.0 6.4 84 6.17 45 6 283.5 300.8 284.6
971.0 315 8.0 5.4 84 5.82 59 8 283.5 299.9 284.5
945.0 537 6.8 3.9 82 5.38 90 13 284.5 299.8 285.4
936.6 610 7.5 3.8 77 5.38 100 14 285.9 301.3 286.9
933.0 641 7.8 3.7 75 5.38 100 14 286.6 302.0 287.5
925.0 712 7.8 3.7 75 5.42 100 13 287.3 302.8 288.2
909.0 856 7.8 4.4 79 5.80 86 10 288.7 305.4 289.7
902.6 914 7.5 4.0 79 5.67 80 9 288.9 305.3 289.9
869.7 1219 5.6 1.7 76 5.01 55 12 290.1 304.7 291.0
852.0 1388 4.6 0.5 75 4.68 64 8 290.8 304.5 291.6
850.0 1407 4.4 0.3 75 4.62 65 8 290.7 304.3 291.6
840.0 1503 4.2 0.1 75 4.61 101 8 291.5 305.1 292.3
812.0 1779 3.0 2.6 97 5.72 206 10 293.1 309.9 294.1
807.0 1829 3.0 2.6 97 5.77 225 10 293.6 310.6 294.6
788.0 2022 3.0 2.8 99 5.98 257 11 295.6 313.3 296.7
777.2 2134 2.4 2.2 99 5.80 275 11 296.1 313.3 297.1
765.0 2262 1.6 1.5 99 5.61 277 17 296.6 313.3 297.6
748.5 2438 2.6 -0.1 83 5.11 280 25 299.5 315.0 300.5
745.0 2476 2.8 -0.4 79 5.01 279 26 300.2 315.4 301.1
731.0 2629 1.6 -3.4 69 4.09 277 30 300.5 313.1 301.2
720.7 2743 0.5 -4.1 71 3.95 275 33 300.5 312.7 301.2
700.0 2976 -1.7 -5.4 76 3.67 270 30 300.6 311.9 301.2
666.0 3370 -4.9 -6.7 87 3.49 264 28 301.3 312.1 301.9
641.9 3658 -6.8 -8.7 87 3.11 260 26 302.3 312.1 302.9
619.0 3942 -8.7 -10.6 86 2.77 232 28 303.3 312.1 303.8
617.4 3962 -8.8 -10.8 86 2.74 230 28 303.4 312.1 303.9
606.0 4106 -9.5 -12.0 82 2.53 239 33 304.2 312.3 304.7
596.0 4235 -7.9 -8.7 94 3.34 248 37 307.5 318.2 308.1
593.5 4267 -8.1 -9.0 93 3.29 250 38 307.7 318.2 308.3
565.0 4649 -10.1 -12.1 85 2.69 247 42 309.7 318.4 310.2
548.4 4877 -11.6 -13.4 87 2.50 245 45 310.5 318.7 311.0
518.0 5313 -14.5 -15.8 90 2.17 241 60 312.1 319.4 312.5
506.3 5486 -15.5 -17.0 88 2.00 240 66 312.9 319.6 313.3
500.0 5580 -16.1 -17.7 87 1.91 240 65 313.4 319.8 313.7
466.4 6096 -19.4 -21.8 82 1.44 245 64 315.5 320.4 315.8
436.0 6596 -22.7 -25.8 76 1.08 245 64 317.5 321.3 317.7
400.0 7220 -27.7 -31.6 69 0.68 245 64 318.9 321.4 319.0
377.8 7620 -31.0 -35.5 65 0.50 250 65 319.8 321.6 319.9
361.7 7925 -33.5 -38.4 61 0.38 250 67 320.4 321.9 320.5
322.0 8741 -40.3 -46.3 53 0.19 250 82 321.9 322.6 321.9
303.4 9144 -43.3 -50.2 47 0.13 250 90 323.1 323.7 323.2
300.0 9220 -43.9 -50.9 46 0.12 250 90 323.4 323.9 323.4
264.0 10067 -51.1 -59.1 38 0.05 246 104 324.9 325.1 324.9
250.0 10420 -54.3 -61.3 42 0.04 245 110 325.2 325.4 325.2
217.8 11278 -61.7 -68.7 39 0.02 250 123 326.8 326.9 326.8
217.0 11302 -61.9 -68.9 39 0.02 250 123 326.9 326.9 326.9
200.0 11810 -66.3 -73.3 37 0.01 250 119 327.6 327.7 327.6
184.0 12311 -70.5 -76.5 41 0.01 255 120 328.7 328.7 328.7
181.0 12409 -70.7 -76.7 41 0.01 255 121 329.9 329.9 329.9
180.0 12442 -69.3 -76.3 36 0.01 255 121 332.7 332.8 332.7
179.0 12476 -64.5 -71.5 38 0.01 255 121 341.1 341.2 341.1
178.4 12497 -62.6 -69.9 37 0.02 255 121 344.6 344.6 344.6
177.0 12545 -58.3 -66.3 35 0.03 257 115 352.4 352.5 352.4
174.0 12654 -55.3 -63.3 36 0.04 263 102 359.0 359.2 359.1
171.0 12765 -55.9 -64.9 31 0.04 268 88 359.8 360.0 359.8
170.0 12802 -55.3 -64.3 32 0.04 270 84 361.4 361.6 361.4
169.0 12840 -54.7 -63.7 32 0.04 271 81 363.0 363.2 363.1
162.1 13106 -55.4 -67.0 22 0.03 280 58 366.2 366.4 366.2
161.0 13151 -55.5 -67.5 21 0.03 278 56 366.8 366.9 366.8
154.5 13411 -57.0 -71.9 13 0.01 265 43 368.5 368.6 368.5
150.0 13600 -58.1 -75.1 10 0.01 260 44 369.8 369.8 369.8
140.2 14021 -60.2 -80.4 5 0.00 240 64 373.3 373.3 373.3
138.0 14122 -60.7 -81.7 5 0.00 241 64 374.1 374.1 374.1
133.0 14351 -61.7 -83.7 4 0.00 244 64 376.3 376.3 376.3
131.0 14444 -60.9 -84.9 3 0.00 245 64 379.4 379.4 379.4
126.0 14685 -62.5 -86.5 3 0.00 247 65 380.7 380.7 380.7
124.0 14784 -61.9 -86.9 2 0.00 248 65 383.6 383.6 383.6
121.0 14935 -63.1 -88.1 2 0.00 250 65 384.1 384.1 384.1
119.0 15038 -62.7 -89.7 2 0.00 253 65 386.6 386.6 386.6
118.0 15090 -61.2 -89.7 1 0.00 255 65 390.3 390.3 390.3
117.0 15143 -59.7 -89.7 1 0.00 259 64 394.0 394.0 394.0
115.2 15240 -59.6 -90.2 1 0.00 265 63 396.0 396.0 396.0
114.0 15305 -59.5 -90.5 1 0.00 266 61 397.3 397.3 397.3
112.0 15416 -57.9 -89.9 1 0.00 268 56 402.3 402.4 402.3
110.0 15530 -58.7 -89.7 1 0.00 270 52 402.9 402.9 402.9
106.0 15762 -58.7 -89.7 1 0.00 274 44 407.2 407.2 407.2
104.0 15882 -57.1 -89.1 1 0.00 276 39 412.5 412.5 412.5
100.0 16130 -57.1 -89.1 1 0.00 280 30 417.1 417.1 417.1
Station information and sounding indices Station identifier: GRB
Station number: 72645
Observation time: 100406/1200
Station latitude: 44.48
Station longitude: -88.13
Station elevation: 214.0
Showalter index: 9.94
Lifted index: 12.54
LIFT computed using virtual temperature: 12.73
SWEAT index: 84.60
K index: 17.10
Cross totals index: 16.40
Vertical totals index: 20.50
Totals totals index: 36.90
Convective Available Potential Energy: 0.00
CAPE using virtual temperature: 0.00
Convective Inhibition: 0.00
CINS using virtual temperature: 0.00
Bulk Richardson Number: 0.00
Bulk Richardson Number using CAPV: 0.00
Temp [K] of the Lifted Condensation Level: 277.08
Pres [hPa] of the Lifted Condensation Level: 910.20
Mean mixed layer potential temperature: 284.64
Mean mixed layer mixing ratio: 5.61
1000 hPa to 500 hPa thickness: 5515.00
Precipitable water [mm] for entire sounding: 22.65

If cooled to whatever the boiling point is at 1/2 atm, the NH3 will condense, giving up latent heat as it does so, but this will be conducted out of the balloon wall, so eventually the NH3 will condense. Note you will have some vapor still because of NH3 vapor and liquid will be in equilibrium.

Very True,

Because the balloon wall is flexible and will apply a pressure of approximately 1 atm to the contents, the NH3 partial pressure will increase as the liquid forms, speeding up the liquefaction.

True, but of course a pressureized balloon is very expensive and hard to make, and if we were to do that then we may as well go with a super pressure design anyway. but this is not an option.

Eventually, you will have half the volume you started with, the same total mass, and half the lift (actually less as the weight of the NH3 liquid is now simply ballast and not contributing to lift).

Exactly

If you are considering the cooling as taking place at high altitude, remember that the atmospheric pressure is far lower, so the boiling point of the NH3 will be much lower also.

True, and this was a problem to me also, But i did find this chart. But i admit to everyone right now I'm terrible making conversions. but this chart looks like it gives the vapor point of NH3 for various levels of vacuum. Now anyone here good crunching numbers? With the above temp profile, and this chart below,, at what level will NH3 condense, if at all?

It may be that you won't get the balloon cold enough to condense the NH3.

Here is that Chart,,

I think the coldest the atmosphere gets is somewhat below -50C. You would have to look up the saturation pressure of NH3 at that temperature and compare it to the atmospheric pressure at that altitude to see if you will get condensation. Remember, the partial pressure is 1/2 the atmospheric pressure at that altitude so you need to have a saturation pressure of NH3 greater than half the local atmospheric pressure for condensation to start.

So armed with the temp profile from this morning, and the vapor pressure chart, will NH3 condense and at what altitude will it?

Thanks Joe

Hi NSS

Because the balloon wall is flexible and will apply a pressure of approximately 1 atm to the contents, the NH3 partial pressure will increase as the liquid forms, speeding up the liquefaction.

True, but of course a pressureized balloon is very expensive and hard to make, and if we were to do that then we may as well go with a super pressure design anyway. but this is not an option.

I meant that the pressure inside will match the local atmospheric pressure at that height. This will apply whether the balloon is elastic or big enough to allow the gas inside to expand the correct amount. I wasn't suggesting a pressurized balloon.

The chart for NH3 vapor pressure is great. I'll see what I can come up with. Got to dredge up conversions from torr to MPa. Looks like the temps are in degrees Kelvin.

Not sure when I'll get on to it so someone else will probably do it first.

I am a chemist who has dealt quite a bit with gases.

The gases will not react. The mixture will be the sum of the volumes of the two gases. If added very slowly to assure no mixing, they will tend to form 2 layers with NH3 at the bottom. However, in the real world this is unlikely and even then would probably not stay that way over time. With mixing, they will form a stable homogeneous mixture that will not separate.

There may be a theoretical way of calculating the amount of condensation at various temperatures and pressures, but it is not straightforward. I don't know if you can find actual data for the specific conditions you desire. Condensation would likely start at somewhat below -33C, but there would be more and more condensation as the temperature is lowered.

1 mole of gas at 0C is approximately 22.4 liters. The average molecular weight of air is 28.8 g/mole. 1 mole of H2 will lift 28.8g-2g=26.8g. 1 mole of NH3 will lift 28.8g-17g=11.8g. So the lifting power of NH3 is 44% that of H2.

Tad

Awesome info Tad.

I was way off on my calculations of the lifting power of NH3 tho.

I went by cubic feet at sea level.

H2 at sea level can lift 1.216 ounces per cubic foot.

Does this mean by your calculations a cubic foot of NH3 at sea level can lift 0.535 ounces?

Joe

My calculations for lifting power are about 10% lower than that given on some websites, so I may be a bit off, but yes, NH3 can lift 44% of what H2 can.

Further, Google mentions that NH3 is commonly used to fill weather balloons because it can be liquefied, so this seems like common practice. Try searching for the terms together, and you will probably get some good practical information.

Tad

Ammonia can be liquified at low pressures and the combined weight of liquid NH3 and container is a lot less than H2 or He compressed to 3000 psi at the same expanded volume if you need to take it to a location for release of a bunch of balloons

Hi Tad,

so, can you break it down like this so I can compare my numbers

say 1 cu ft of each below will lift how much in ounces?

H2

HE

NH3

Joe

I just want to keep watching this interesting discussion. As an electronic engineer- I have little knowledge.

However - for my own understanding

1) in metallurgy I came across iron-carbon diagram and how melting temperature varied with mixture of iron and carbon. Doesn't something similar happen in a gas mixture like this?

2) Tad has made a valuable calculation. Ideal gas equation PV = nRT must be applicable to this case - am I right?

1) That is correct; gas properties is function of gases concentration.

2) Ideal equation only applies for gas mix where interaction as so weak and phase equilibrium doesn't change; PVT variation affects these interactions and equilibrium as well.

For a good illustration as to how gases in a flexible-walled container, check out Andrew Szydlo’s Christmas lectures to the Royal Institution, which can be found on YouTube.