Counting NaOH dissociation entalphy problem

NaOH dissociation is exothermic so ΔH<0



But when I have a reaction

NaOH(s) => Na+(aq) + OH-(aq)



and count ΔrH using standard entalphy change of formation:

ΔfH (NaOH) = -425 kj/mol

ΔfH (OH-(aq)) = -230 kj/mol

ΔfH (Na+(aq)) = +242 kj/mol

Data from Atkins phisical chemistry basics



ΔrH= ΔfH (products) - ΔfH (substrates) = (-230 + 240,12) - (-425) = +435,12 kj/mol

From this calculation it seems that reaction is pretty endothermic and that's surely not true.



Can someone tell me where am I making mistake ?