# Microwaving liquid N2 **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [January 15, 2003, 12:24am UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637 "2003-01-15T00:24:32Z")\ **Posts on this page:** 14\ **Page:** 2
**Author:** ![Duck\_Duck\_Goose](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)\ **Post date:** [January 18, 2003, 10:22pm UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/21 "2003-01-18T22:22:42Z")
Thank you, both, but I have to say that John’s explanation was more fun, all those dancing molecules. 😃 ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [January 22, 2003, 6:52pm UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/22 "2003-01-22T18:52:01Z")
> [@](#): > > _ **Christopher** said:_ > I can’t imagine that water is particularly soluble in N2, so it will quickly freeze and drop to the bottom. Solid water is denser than liquid nitrogen? ---
**Author:** ![antechinus](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@antechinus](https://boards.straightdope.com/u/antechinus)\ **Post date:** [January 23, 2003, 1:05am UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/23 "2003-01-23T01:05:52Z")
I thought the absorption of microwave frequencies was due to **rotation** of the molecule. If the molecule is polar, like H2O, then the molecule will tumble as the EM wave ‘passes by’. The dipole interacts with the oscillating electric field. If the molecule is non-polar, like N2, then the electric field component of the EM radiation does not affect the molecule. Vibrational frequencies are usually in the infra-red region. ---
**Author:** ![Wikkit](https://avatars.discourse-cdn.com/v4/letter/w/c0e974/32.png) [@Wikkit](https://boards.straightdope.com/u/Wikkit)\ **Post date:** [January 23, 2003, 4:07pm UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/24 "2003-01-23T16:07:08Z")
> [@](#): > > \*Originally posted by Sunspace \* > \*\*Solid water is denser than liquid nitrogen? \*\* Yep. Ice is about .92 g/cm[sup]3[/sup], liquid nitrogen is about .8 g/cm[sup]3[/sup] ---
**Author:** ![bbeaty](https://avatars.discourse-cdn.com/v4/letter/b/c0e974/32.png) [@bbeaty](https://boards.straightdope.com/u/bbeaty)\ **Post date:** [January 26, 2003, 11:05pm UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/25 "2003-01-26T23:05:22Z")
> [@](#): > > OK, now, you know the classic schtick where an opera singer hits a note and makes a glass shatter? Well, that’s how a microwave oven works. It makes those water molecules (which are in all food) dance around like crazy – presto! instant heat! Hey, explanations I’ve seen have stressed the fact that liquid water DOESN’T have resonances. The weak bonds between the molecules spoil any resonant effects. Yes, water VAPOR (especially in vacuum) is going to have sharp resonances and absorbtion lines. But don’t assume that the same applies to liquids. Analogy: a bronze bell has a narrow resonance line, but if you bury it in dirt the resonance is spoiled. Now water molecules are certainly polar, and if exposed to strong e-fields will tend to rotate (which disrupts the bonds to neighboring molecules, so strong rotation will heat up the liquid.) But this effect isn’t frequency dependent. We could just as well place our mug of coffee right near the antenna of a 1000 watt UHF transmitter and the radio waves would heat it just as hot. The rule is that “polar molecules are heated by high frequency e-fields”, as opposed to “resonant molecules absorb EM energy of a particular frequency.” I think the stuff about water resonance is a kind of “urban legend” among technical people. It probably started out because of those water absorbtion lines found in interstellar space by radio astronomers. But that only applies to single molecules, those not in contact with neighbors. ---
**Author:** ![Truth\_Seeker](https://avatars.discourse-cdn.com/v4/letter/t/5fc32e/32.png) [@Truth\_Seeker](https://boards.straightdope.com/u/Truth_Seeker)\ **Post date:** [January 27, 2003, 9:21pm UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/26 "2003-01-27T21:21:01Z")
Very true, **bbeaty**. I knew some people who worked in a facility that designed and tested high powered radars. Sometimes, just for kicks, they’d stick their lunches in the anechoic chamber and fire up whatever radar they were testing. Not the most efficient use of a multi-million dollar piece of equipment, perhaps, but an entertaining one. ---
**Author:** ![antechinus](https://avatars.discourse-cdn.com/v4/letter/a/fbc32d/32.png) [@antechinus](https://boards.straightdope.com/u/antechinus)\ **Post date:** [January 28, 2003, 4:46am UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/27 "2003-01-28T04:46:21Z")
> [@](#): > > \*Originally posted by bbeaty \* > \*\*Hey, explanations I’ve seen have stressed the fact that liquid water DOESN’T have resonances. The weak bonds between the molecules spoil any resonant effects. > > Yes, water VAPOR (especially in vacuum) is going to have sharp resonances and absorbtion lines. But don’t assume that the same applies to liquids. Analogy: a bronze bell has a narrow resonance line, but if you bury it in dirt the resonance is spoiled. > > Now water molecules are certainly polar, and if exposed to strong e-fields will tend to rotate (which disrupts the bonds to neighboring molecules, so strong rotation will heat up the liquid.) But this effect isn’t frequency dependent. We could just as well place our mug of coffee right near the antenna of a 1000 watt UHF transmitter and the radio waves would heat it just as hot. The rule is that “polar molecules are heated by high frequency e-fields”, as opposed to “resonant molecules absorb EM energy of a particular frequency.” > > I think the stuff about water resonance is a kind of “urban legend” among technical people. It probably started out because of those water absorbtion lines found in interstellar space by radio astronomers. But that only applies to single molecules, those not in contact with neighbors. \*\* The term ‘resonance’ usually applies to coupling of oscillators. It is better to use ‘absorption’ in the descriptions here. Liquid water still does absorb in the infrared region, however liquid water has a broadened and shifted absorption band due to intermolecular forces. -O-H…O-H…O- (close enough for just one line) So I dont think the bell analogy isn’t very good. I think more in terms of balls on springs. Continuing the analogy with liquid water, maybe the balls/springs have crazy-string sprayed over them. Pure rotational transitions are in the microwave region. Water has a permanent dipole and thus shows a pure rotational spectrum. ie it absorbs microwave. Nitrogen does not. Also, nitrogen has no vibrational mode \* that changes the dipole moment\* and thus cannot absorb in the IR region either. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [January 28, 2003, 2:35pm UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/28 "2003-01-28T14:35:06Z")
> [@](#): > > \*Originally posted by bbeaty \* > \*\*Hey, explanations I’ve seen have stressed the fact that liquid water DOESN’T have resonances. The weak bonds between the molecules spoil any resonant effects. > > Yes, water VAPOR (especially in vacuum) is going to have sharp resonances and absorbtion lines. But don’t assume that the same applies to liquids. Analogy: a bronze bell has a narrow resonance line, but if you bury it in dirt the resonance is spoiled. > > Now water molecules are certainly polar, and if exposed to strong e-fields will tend to rotate (which disrupts the bonds to neighboring molecules, so strong rotation will heat up the liquid.) But this effect isn’t frequency dependent. We could just as well place our mug of coffee right near the antenna of a 1000 watt UHF transmitter and the radio waves would heat it just as hot. The rule is that “polar molecules are heated by high frequency e-fields”, as opposed to “resonant molecules absorb EM energy of a particular frequency.” > > I think the stuff about water resonance is a kind of “urban legend” among technical people. It probably started out because of those water absorbtion lines found in interstellar space by radio astronomers. But that only applies to single molecules, those not in contact with neighbors. \*\* Well, sort of right, sort of wrong. Liquid water has an absorption spectrum with definite peaks and troughs in it. It _is_ frequency dependent. And some of the peaks _are_ sharp enough to be called “resonant frequencies”. [Cite.](http://www.sbu.ac.uk/water/vibrat.html) Look especially at the absorption peak at around 3 um. The closest peak to the 2.45 GHz operating frequency is at about 10 GHz for liquid water at 0 [sup]o[/sup]C, rising to 100 GHz for liquid water at 100 [sup]o[/sup]C. [Cite](http://www.sbu.ac.uk/water/microwave.html) ---
**Author:** ![fgarriel](https://avatars.discourse-cdn.com/v4/letter/f/c6cbf5/32.png) [@fgarriel](https://boards.straightdope.com/u/fgarriel)\ **Post date:** [January 28, 2003, 2:44pm UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/29 "2003-01-28T14:44:03Z")
OT: I love this place. I rarely have anything to contribute, but so much to absorb (or is it resonate? ;)) ---
**Author:** ![user\_hostile](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/user_hostile/32/474_2.png) [@user\_hostile](https://boards.straightdope.com/u/user_hostile)\ **Post date:** [February 6, 2003, 4:45pm UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/30 "2003-02-06T16:45:26Z")
About ten years ago, I took a 1 pint plastic bottle with a flip-top and filled it about a 1/4 full. Then, I took some liquid Nv2 and poured enough to fill it up half way. The Nv2 was floating above the water (as I expected) and boiling away furiously and spraying a large vapor trail out of the container. I reasoned that if the water was between the plastic and Nv2, it keep the container becoming brittle. I closed the flip-top and threw it into a large trash container figuring it would give a loud pop. Well, as I found out the hard way that flash boiling in a closed container was a very bad idea. I didn’t get hurt, fortunately, but I won’t do it again either. :eek: ---
**Author:** ![user\_hostile](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/user_hostile/32/474_2.png) [@user\_hostile](https://boards.straightdope.com/u/user_hostile)\ **Post date:** [February 6, 2003, 5:07pm UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/31 "2003-02-06T17:07:05Z")
**Change:** _From:_ “I reasoned that if the water was between the plastic and Nv2, it keep the container becoming brittle.” _To:_ “I reasoned that if the liquid Hv2Owater was between the plastic wall and the liquid Nv2, it would keep the container from becoming brittle.” :rolleyes: ---
**Author:** ![bbeaty](https://avatars.discourse-cdn.com/v4/letter/b/c0e974/32.png) [@bbeaty](https://boards.straightdope.com/u/bbeaty)\ **Post date:** [February 15, 2003, 4:18am UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/32 "2003-02-15T04:18:48Z")
> [@](#): > > \*Originally posted by Desmostylus \* > **Well, sort of right, sort of wrong. Liquid water has an absorption spectrum with definite peaks and troughs in it.** I’m talking about the frequency where most microwave ovens operate. Wasn’t that clear? > [@](#): > > \*\*It _is_ frequency dependent. And some of the peaks _are_ sharp enough to be called “resonant frequencies”. [Cite.](http://www.sbu.ac.uk/water/vibrat.html) Look especially at the absorption peak at around 3 um. > \*\* That’s long IR!!! What does that have to do with microwave ovens purportedly being set to a resonance peak? I bet water has UV and gamma absorbtion lines, but that has no bearing on my previous message either. > [@](#): > > \*\*The closest peak to the 2.45 GHz operating frequency is at about 10 GHz for liquid water at 0 [sup]o[/sup]C, rising to 100 GHz for liquid water at 100 [sup]o[/sup]C. [Cite](http://www.sbu.ac.uk/water/microwave.html) \*\* In other words, “I’m right.” 🙂 Read my original message. I’m was complaining about people who claim that microwave ovens heat water because of resonance. In reality your kitchen oven’s frequency is NOT set to a water resonance peak. If it was, then the radiation wouldn’t penetrate bulk water such as meat, coffee, etc. And besides, interactions between water molecules spoil the peaks in the many-cm band so they aren’t even absorbtion lines, they’re huge broad humps. Microwave ovens work by having the polar molecules trying to follow an e-field, they aren’t pumping a molecular resonance. Your cites say as much. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [February 15, 2003, 5:15am UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/33 "2003-02-15T05:15:35Z")
> [@](#): > > \*Originally posted by bbeaty \* > **Yes, water VAPOR (especially in vacuum) is going to have sharp resonances and absorbtion lines. But don’t assume that the same applies to liquids.** I was pointing out that the same _does_ apply to liquids. > [@](#): > > \*Originally posted by bbeaty \* > **But this effect isn’t frequency dependent. We could just as well place our mug of coffee right near the antenna of a 1000 watt UHF transmitter and the radio waves would heat it just as hot.** As I pointed out, the effect _is_ frequency dependent. > [@](#): > > \*Originally posted by bbeaty \* > \*\*I think the stuff about water resonance is a kind of “urban legend” among technical people. It probably started out because of those water absorbtion lines found in interstellar space by radio astronomers. But that only applies to single molecules, those not in contact with neighbors. \*\* Again, I pointed out that it _does_ apply to liquids. > [@](#): > > \*Originally posted by bbeaty \* > **I’m talking about the frequency where most microwave ovens operate. Wasn’t that clear?** No, it wasn’t, especially when you were talking a complete lack of frequency dependence. I guessed that that _might_ be what you were talking about, which was why _I_ mentioned the operating frequency. The two specific points I addressed were: 1. Water vapour might resonate, but liquid water doesn’t. 2. RF absorption by liquid water is independent of frequency. On both points, you were simply wrong. > [@](#): > > \*Originally posted by bbeaty \* > > > [@](#): > > > > The closest peak to the 2.45 GHz operating frequency is at about 10 GHz for liquid water at 0 [sup]o[/sup]C, rising to 100 GHz for liquid water at 100 [sup]o[/sup]C. Cite > > \*\*In other words, “I’m right.” > > Read my original message. I’m was complaining about people who claim that microwave ovens heat water because of resonance. In reality your kitchen oven’s frequency is NOT set to a water resonance peak. If it was, then the radiation wouldn’t penetrate bulk water such as meat, coffee, etc. And besides, interactions between water molecules spoil the peaks in the many-cm band so they aren’t even absorbtion lines, they’re huge broad humps.\*\* If you wanted to be right, and you wanted to say something like that, then you should have just said something like that. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [February 15, 2003, 5:21am UTC](https://boards.straightdope.com/t/microwaving-liquid-n2/148637/34 "2003-02-15T05:21:19Z")
In other words, I understood the point you were _trying_ to make, but disagreed completely with the generalisations and mistakes you made along the way. [Previous page](https://boards.straightdope.com/t/microwaving-liquid-n2/148637.md?page=1)