What is the standard enthalpy of formation of HCl (aq)?Help much appreciated!

HCl can exists in two forms. It is either in aqueous or in gaseous form. It can be formed from Hydrogen and chlorine ions or gasses. 

Hydrogen Chloride aqueous delta H f = -92.30

Hydrogen Chloride gaseous delta H f = -167.2

examples of production of HCl

Aqueous HCl can be produced in our stomach from Carbon dioxide and Water as starting material.

CO2 + H2O ---> H2CO3

carbonic acid produces proton

H2CO3 <---> H+  +  HCO3-

That can combine with the freely floating Cl- ion in the cell thus producing HCl.

Gaseous HCl can be produced via burner process. This is an exothermic reaction.

H2 (gas) + Cl2 (gas) --> HCl (gas)