Enthalpy of mixing for an ideal dilute solution

In view of the definition of an ideal dilute solution, we can write that  

given relation [A.2.24] (see Appendix 2), we have where, for the solvent  

The partial molar enthalpy of the solvent is identical to its molar enthalpy in the pure state in the same state of aggregation as the solution. 

the constant appears as the partial molar enthalpy of mixing of the solute s in the solution, which enables us to write the following, in light of relation [2.29]  

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