The reaction for which we have to find the enthalpy change is: C2H3OH(l)-->CH3OCH3(l)
The Enthalpy of formation of C2H3OH(l) is given as DHo=-1234.7 kJ and the enthalpy of formation of CH3OCH3(l) is given as DHo=-1328.3kJ.
For a reaction A --> B, the enthalpy change DH of the reaction is given by DHb - DHa
Using the values we have here, DHb = -1328.3 kJ and DHa = -1234.7 kJ, DH of the reaction is -1328.3 - (-1234.7) = -1328.3 + 1234.7 = -93.6 kJ.
The change in enthalpy when the reaction C2H3OH(l)-->CH3OCH3(l) occurs is -93.6 kJ. As the change in enthalpy, DH is negative for this reaction, it is an exothermic reaction that releases heat when it takes place.