From the following data at 25^{\circ} {C}, calculate the ∆_{r} {H}^{0} for {H}_{2} {O}( {g}) \to 2 {H}( {g})+ {O}( {g}). reaction: ∆_{r} {\H}^{0}( {\kJ} {\mol}^{-1}) \frac{1}{2} {H}_{2}( {g})+\frac{1}{2} {O}_{2}( {g}) \to {OH}( {g}) 42.09 {H}_{2}( {g})+\frac{1}{2} {O}_{2}( {g}) \to {H}_{2} {O}( {g}) -242 {H}_{2}( {g}) \to 2 {H}( {g}) 436 {O}