# If water is exposed to high voltage, it will ionize.

## Main Question or Discussion Point

if water is exposed to high voltage, it will ionize. What is the minimum voltage needed for that to happen? Thanks!

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Andrew Mason
Homework Helper
if water is exposed to high voltage, it will ionize. What is the minimum voltage needed for that to happen? Thanks!
What is the energy required to remove an electron from a hydrogen or oxygen molecule?

AM

Gokul43201
Staff Emeritus
Gold Member
What is the energy required to remove an electron from a hydrogen or oxygen molecule?

AM
This will only give you an estimate of the ionization potential for H2O(gas). In the liquid state, the number is much lower, due to several effects that are not easy to calculate (you can think of these as described by a local dielectric constant). I believe the number for water is about 1 volt.

EDIT: Yup, the standard reduction potential tables tell me it's 0.83V

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so, say a circuit is submerged in the water. The circuit requires only a 0.83V to ionize the surrounding waters?!? Wow! I though it wouold be much higher than that!

disregardthat
Wasn't that for 1 molecule?
So if you had millions of molecules it'd take millions of volts right?

Andrew Mason
Homework Helper
so, say a circuit is submerged in the water. The circuit requires only a 0.83V to ionize the surrounding waters?!? Wow! I though it would be much higher than that!
Multiply that by the number of coulombs of charge to get the energy. So the energy to remove an electon from a water molecule in the liquid state is .83eV or .83 x 1.6e-19 C = 1.3e-19 Joules.

AM

Wasn't that for 1 molecule?
So if you had millions of molecules it'd take millions of volts right?
so is this true? Thanks!

Gokul43201
Staff Emeritus
Gold Member
No, it's not. It does not take 2 million volts to produce hydrogen from the electrolysis of water (it takes about 2 volts). The Daniell (Cu|CuSO4||ZnSO4|Zn Galvanic) cell produces an EMF of about 1.1V (not millions, billions or an Avogadro number of volts).

The real number will be about 1 or 2V. There will be a deviation from the ideal ionization potential, in a real electrolytic cell, that depends on the electrodes used. An ideal, inert electrode will get you closest to the ideal number. Any other electrode will require an overvoltage to produce the same current as the ideal cell.

sunchips said:
so, say a circuit is submerged in the water. The circuit requires only a 0.83V to ionize the surrounding waters?!? Wow! I though it wouold be much higher than that!
Heard of anyone that killed their cell phone by dropping it in water? Typical phone batteries run at somwhere between 3V and 4V - easily enough to ionize a path through water (if the phone case isn't watertight) and make a short.

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I'm sorry..I think I didn't explain my situation well enough. I am asking, in terms of say....

suppose we have a heating element submerged in water. (e.g. a coffee maker, or amny other possible everyday things). When the current is passed through the nichrome heating element, will the current ionize the surrounding waters? is it powerful enough?

Sorry if I didnt explain myself well before, and thanks for all your help!

Gokul43201
Staff Emeritus
Gold Member
I'm sorry..I think I didn't explain my situation well enough. I am asking, in terms of say....

suppose we have a heating element submerged in water. (e.g. a coffee maker, or amny other possible everyday things). When the current is passed through the nichrome heating element, will the current ionize the surrounding waters? is it powerful enough?
To the best of my knowledge, all immersion heaters have an electrically insulating (but thermally conductive) coating over the nichrome element. I'd expect the outer case to be grounded.