Calculating heat released from excess enthalpy

[rwooduk]

Hello,

I am currently trying to determine the method to calculate the heat absorbed / released when a gas and liquid mix. I believe that this is known as the heat/enthalpy of mixing (or excess molar enthalpy). I also believe, that if this value is negative it means an exothermic reaction (heat released), if the value is positive it means an endothermic reaction (heat absorbed).

I'd really appreciate some direction on where to go from here. How would I calculate the actual heat absorbed/released from the heat of mixing value.

Thanks for any help.