How does one estimate the standard heat of formation of organic compounds which contain the -SO3Na group? An example of such a compound is the sodium salt of benzenesulphonic acid (also called sodium benzenesulfonate). What is the value (in units such as kJ/gmol, kcal/gmol, kJ/kg or kcal/kg) of the contribution to the standard heat of formation by the -SO3Na group? Please suggest any group contribution method which can solve this problem.