What is the answer for: Calculate the energy needed to split the water in 2H2O ------- 4H + 2 O into H and O s?

Question

also calculate  the energy change when H and  O stoms join to form  H2 and  O2 molecules  in 
4H+ 2) -------- 4h2 + O2

BII · Accepted Answer

(You have some typos)
2H2O → 4H  +  2O  ∆H(rxn)  
Can ∆H(rxn)  be estimated as 4∆H(O-H) the accepted value of the O-H bond energy? 
O-H = 459 kj mol^-1 [1] Hence ∆H(rxn)  = 4×459 = +1836 kJ =ve heat needed to be put into system 
4H+ 2O → 2h2 + O2
∆H(rxn)  = 2∆H(H-H) + ∆H(O-O)   taking values from 1  
∆H(rxn = 2×432 + 494 = -1358 kJ
[1] http://www.wiredchemist.com/chemistry/data/bond_energies_lengths.html

What is the answer for: Calculate the energy needed to split the water in 2H2O ------- 4H + 2 O into H and O s?

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