Provided that I know the enthalpy of formation $\Delta H_f^0(X_{g})$ of a substance $X$ in gas phase and its enthalpy of dissolution $\Delta H^0_{sol}(X)$ in the same conditions, considering that the dissolution reaction is $X_g \leftrightharpoons X_{aq}$ is it legit to consider that the enthalpy of formation of that substance $X$ in aqueous phase would be $\Delta H^0_f(X_{aq}) = \Delta H^0_{sol}(X) - \Delta H_f^0(X_{g})$?

As a concrete exemple, considering that the enthalpy of formation of $H_2$ in gas phase is 0 kJ/mol and that its enthalpy of dissolution is approximately -4.15 kJ/mol (using the data provided here), can we conclude that the enthalpy of formation of $H_2$ in aqueous phase is approximately -4.15 kJ/mol?

  • $\begingroup$ That seems correct. $\endgroup$ – Buck Thorn Aug 21 '19 at 17:13

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