Trevor Hodgson
Former Project Manager (1975–2000)
Let us consider 1.0 L of water
<olar mass water 18g/mol
Mass of 1.0L water = 1000 g
Mol H2O in 1.0 L = 1 000 g / 18 g/mol = 55.55 mol
If H2O is subjected to electrolysis, the following occurs
2H2O ↔ 2H2 + O2
2 mol H2O will produce 1 mol O2
The 55.55 mol water from the litre will produce 55.55/2 = 27.8 mol O2
At normal temperature and pressure , 1 mol O2 has volume 24.5 L
The 27.8 mol O2 has volume = 27.8 mol * 24.5 L/mol = 681 L O2
Normal air is +/- 20% O2
You have sufficient oxygen to regenerate 681 L * 4 = 2,724 L of ”stale” gas that has been totally depleted of O2 . You will produce 3,400 L of breathable air. How long will this support life. I have no idea. But it is a practical proposition to recover oxygen from water in a closed environment such as a space craft.
Dan Miller
Jul 12
The amount of air in 1 gallon or 1 liter of water is negligible. Water is primarily composed of hydrogen and oxygen molecules, with no significant amount of trapped air.
Using electrolysis to split water into hydrogen and oxygen can indeed be a viable approach for generating breathable air in space or other isolated environments. Here's a more detailed explanation:
One gallon (3.785 liters) of water can be split into approximately 0.4 cubic meters of hydrogen gas and 0.2 cubic meters of oxygen gas through electrolysis.
The resulting hydrogen and oxygen can then be recombined in a fuel cell to generate electricity and produce water, which can be reused in the electrolysis process.
The oxygen produced can be used for breathing, while the hydrogen can be used for various other purposes, such as generating electricity or propulsion.
Assuming an average adult human requires approximately 0.84 cubic meters of oxygen per day for respiration, the oxygen produced from 1 gallon (3.785 liters) of water could theoretically sustain one person for about 9 days.
However, in practice, the efficiency of the electrolysis and fuel cell processes, as well as other factors such as leakage and system maintenance, would need to be taken into account, reducing the actual duration of the life support system.
Nevertheless, the principle of using electrolysis to split water and generate breathable oxygen is a well-established concept and has been successfully demonstrated in various space missions and research projects. The specific duration and efficiency would depend on the scale and design of the overall life support system.
Ed Thaxton
M.S. in Mechanical Engineering & Robotics, University of Rhode Island
There is no air, but there are about 2,350 liters of oxygen.
A gallon of water has a mass of 3.785 kg or 8.8 lbs weight (on Earth). A water molecule has two hydrogen atoms and one oxygen atom, with atomic weights, 1 and 16 respectively. Thus the atomic mass of water is 18.
Oxygen at standard temperature and pressure (STP, 0C and 10^15 Pa (one bar)) is 1.429 g/liter.
Hydrogen at STP is 0.08988 g/liter
Water has a atomic mass of 18, made up of 16 parts oxygen an 2 parts hydrogen by mass.
If you just separate out the oxygen then:
(16/18) parts oxygen/water * 3,785g water / 1.429 g/liter = 2,354.4 liters of oxygen at STP
How long this will last depends on what level of CO2 you can tolerate, but a human consumes about 500 liters of oxygen a day. So one person, less than five (5) days.