Splitting H2O?

If I split H2O into Hydrogen %26amp; Oxygen how can I work out how much energy it would take to split it, compared with how much energy I would get recombining it.Splitting H2O?
look up the enthalpy of formation of water, which is -285.83 kJ/mol. that means when water forms from hydrogen and oxygen it gives of 285.83 kJ of heat energy to make one mole. the reverse process to break it up would be putting 285.83 kJ into 1 mole of water to break it up into its compoundsSplitting H2O?
Split water by electrolysis.





With the circuit make a note of the voltage and current used. Also make a note of the time the current is passed.


Make a note of the volumes of each gas produced over the time.





Work out the energy used.


Volts x amps will give the watts used over the period.


it is just then a matter of working out the watt hours to produce 22.5 litres of hydrogen.
You need to know the standard enthalpies of formation, and the balanced equation, and how many moles of water you are starting out with. And remember this is all theoretical.





We will assume 1 mole or 18 g of H2O to begin with to make the conversions easier





We have H2O = H2 + O2





Balancing the equation gives us





2H2O = 2H2 + O2





The standard enthalpies of formation for the oxygen and hydrogen are both 0 kJ/mol





And for liquid water it is -285.8 (the value varies slightly for water vapor (g))





So the change in enthalpy is 0 - 2(-285.8) = 571.6 kJ/mol