why does microwave radiation heat water and current split water into hydrogen and oxygen?..tia sal

The two effects are totally different and are largely unrelated. Microwave heating causes friction of liquid bipolar molecules.

Faraday's law lets current cause a pair of electrochemical reactions that adds an electron to each hydrogen atom and removes two electrons from each oxygen atom, allowing their separation.

Electrolysis normally only responds to the dc component of any current waveform since it is an integration. But the cells can be highly nonlinear which might do an inefficient rectification of ac terms.

Because of a thermodynamic property called "exergy", electrolysis is totally useless for bulk energy hydrogen production when driven from high value grid or pv sources.

Electolysis: Ripping off electrons from OH- and giving them to H+ is just a matter of electrical potencial. With enough voltage, all kinds of redox transformation will happen. Vibrations and frequency have absolutely nothing to do with it. Nothing whatsoever - a DC current from your car batery is perfectly good for the purpose.

Microwawes: microwaves heat thing that have some charge or dipole to them (so that they can absorb the radiation). Water molecule is a dipole. The radiofrequency here is important because different molecules /ions have different absorbtion maxima in microwawe region. It just happens that the microwave photons are in energy region which corresponds transitions between various rotation/translation states of common molecules.

No. A direct-current voltage below, IIRC, 1.2 V will only heat water, like microwaves.

--- Graham Cowan, former hydrogen fan

Only a band of microwave radiation heats water, not all frequencies. All molecules with more than one atom have certain resonent frequencies. The bonds between the atoms are kind of springy, giving rise to the resonent vibrations. If an electromagnetic wave with that same frequency impinges on the molecule, it excites the molecule. It then transfers energy to it, heating it.

The microwave photons in a microwave oven do not have enough energy to ionize (strip electrons from the molecule, or SPLIT the molecule). One needs to get up into the ultraviolet wavelengths/frequencies to get energic enough photons to do that. I am not a spectroscopist, but I assme there are UV wavelengths that will disassociate water.

Heres a hint, when you see steam, it's not that the water has been split into hydrogen and oxygen, but that it has been heated to the point where it becomes gaseous water.

Radiation (of any sort) and electrolysis are two completely different things- why would one expect them to have the same effect? (A DC voltage, by the way, doesn't vibrate.)

The most simplistic explanation for a layman is that the disassociation forces induced into the water by the microwave r.f. field is essentially a.c. at a frequency that if the ions of water are disassociated, the field reverses so quickly that the ions haven't time to move away from each other and consequently recombine.

You can disassocate water using low frequency a.c. at say 60-Hz, but then the cathode and anode are reversing positions at this 60-Hz rate, creating a mix of hydrogen and oxygen at each terminal.

This is why nothing but d.c. is employed for the practical electrolysis of water, simply because the anode and cathode remain fixed negating the ion velocity in the electrolytic solution and allowing hydrogen to collected at the cathode and oxygen at the anode.

For the more technically inclined reader, there have been experiments done using r.f. frequencies to disassociate the water molecule, while using a static electrical field to collect and separate them. IIRC, the conclusion was that there was no net benefit over using simple electrolysis because you're simply trading off Ohmic power loss for microwave production power losses. Hence, if you want to separate water into hydrogen and oxygen, simple d.c. driven electrolysis remains the most efficient way to do the job.

Either way, splitting a water into it's constituent components is and well defined in the literature. Above and beyond this is that you have additionally provide for the losses associated with the specific method that you are using.

Either way, you cannot produce more energy from hydrogen than that which went into producing it, only vary the amount of energy that is alway lost in the chosen process.

Hope this helps. Harry C.

Oh, I in my pontification I nearly missed your original question.

The answer is that microwaves heat water by whatever mechanism agitates and imparts energy to the water molecules.

The heating effect of microwaves has amost nothing to do with splitting water into hydrogen and oxygen, although that may play a role in the agitation of the water molecules.

Harry C.

Check out microwaves and OH bonds Check out electrolysis of water.

Totally different things going on here :)

Bruce

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Caution ===== followups may have been changed to relevant groups (if there were any)

Even at 60Hz, the H shaped electrolysis apparatus shown in chemistry books is poor at producing H2 O2 mixtures compared to using dc. As soon as an electron is transferred, the reversal of voltage takes it away. At microwave frequencies, there is no electrolysis to speak of. Even the mobility of electrons at those frequencies is virtually nil.

What microwaves can do is excite vibration and rotation and vibrational modes. That excitation will heat other modes as the system reaches thermal equilibrium. That is based upon what is called equipartition. That is based upon classical statistical mechanics and has to be modified to take quantum effects into account. Look up the Debye theory of specific heats.

Bill

microwave ovens don't heat water by conduction, (they do heat some special cookware by conduction though)

the frequency of the microwave radiation matches the bending oscilaton frequency of the water molecules, the microwave radiation makes the water molecules it hits ring and bang into each other this is being hotter.

basically water molecules are like tuning forks and the microwaves are on the frequency that makes the fork sing.

Bye. Jasen

Thus, wet coax is a fine cable for various microwave frequencies? Hmm... experience tells otherwise.

Thomas

emitting strong low band energy across a surface of rust can generate M-wave energy depending on the surface texture. so those that have rusty cars and such, better get it to the body shop quick! :)

If all microwave frequencies were absorbed by water, microwave radars wouldn't be able to see through clouds or rain. Now, with IR that is true. Thermal imagers all suffer when humidity is high- not all radars do.

coax doesn't carry microwave radiation.

apart from conducting the electric component of the signal dampness also messes with up the characteristic impedance of the cable....

Bye. Jasen

Yes, there ARE UHF/microwave coaxes, using polyethylene, that will handle the lower bands of microwave, like C and even S bands, as long as you are not going too far. Waveguides may be better, but if you accept some loss, coaxes will work. Not all waveguides are equal, either. Cheap waveguides have attenuation losses too.

However, the statement about the dampness affecting electrical properties of insulating medium is correct.