[zerokun]

Q7.1(a) pg 235 - At 2257 K and 1.00 atm total pressure , water is 1.77 % dissociated at equilibrium by the way of the reaction 2H₂O -> 2H₂ + O ₂ . Calculate K, molar G , del.(delta)G at this temperature.

This is my way of working it .
molar G = -2 X molar H₂O = -2 X -228.57 = 457.14 J/mol = 457.14 X 10³ kJ/mol

Since is equilibrium (dissociation ) , therefore del.G = 0
del.G = molar G + RT ln K
del.G =0, -molar G = RT ln K
457.14 X 10³  = 8.314X 2257 ln K
K = 2.63 X 10^-11

Which is wrong,
the answer given in book is  K =2.85 X 10^-6
I don't know what is wrong with my calculation

[Borek]

Looks to me like K can be calculated from simple stoichiometry of the reaction equation.