Reactions involving gold have been of particular interest to alchemists. Consider the following  reactions,

$\mathrm{Au}(\mathrm{OH}{)}_3+4\mathrm{HCl}⟶{\mathrm{HAuCl}}_4+3{\mathrm{H}}_2\mathrm{O}$ , $\mathrm{\Delta }H=-28\mathrm{kcal}$

$\mathrm{Au}(\mathrm{OH}{)}_3+4\mathrm{HBr}⟶{\mathrm{HAuBr}}_4+3{\mathrm{H}}_2\mathrm{O}$, $\mathrm{\Delta }H=-36.8\mathrm{kcal}$

In an experiment there was an absorption of $0.44 \mathrm{kcal}$when one mole of ${\mathrm{HAuBr}}_4$ was mixed with 4 moles of $\mathrm{HCl}$. Then the fraction ${\mathrm{HAuBr}}_4$ converted into ${\mathrm{HAuCl}}_4$ : (percentage conversion)