Answer to Question #10742 in Physical Chemistry for austentic

Question

I have a sheet on Hess's Law where Enthalpy change is sometimes given as kJ and other times kJ/mol.
Why? What's the difference?

The latter is given as "The heat of vaporisation of water is 44kJ/mol. Calculate the heat of reaction [gaseous ethanol]..."
Why is it kJ/mol and should the heat of reaction be given as kJ or kJ/mol?

Answer 1

The Enthalpy change is usually indicated in kJ/mol. Sometimes it is kJ, but
means kJ/mol ("per mol" is omitted). Hence, the heat of reaction should be given
as kJ/mol. This comment is refer to Hess's Law. In the other cases it is
possible another means (for example, if we should to find the Enthalpy change
for calculated quantity (moles) of substanse).