Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: chris on 22/05/2017 12:54:58
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Rohith wants to know:
The formation of water releases lots of energy, which means the gas molecules of hydrogen and oxygen combine together to form a liquid state of matter. Now, will this liquid [water] take up the same energy to get dissociated back into its constituent gases i,e hydrogen and oxygen?
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Yes, The same amount of energy is involved going both ways. In the practical sense however, you will always need to expend more energy separating them then you can usefully extract from combining them.
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To clarify @Janus point, you need more energy to split them apart because the system is "lossy" - there will be inefficiencies in the process e.g. resistance in the wires used for electrolysis - so that the energy "in" ends up being more than you recover as energy "out" when burning the hydrogen and oxygen.
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Yes, it takes at least as much energy to split water into O2 and H2 as is released when these gases combine to form water.
This is about 260 kJ per mole of water or just shy of 5 eV per molecule of water (4 electrons times 1.23 V). Splitting one liter of water would take at least 16 MJ (4.4 kWh), which is more energy than it would take to launch a liter of water into deep space!