Herein, we present a semiquantitative thermal study of the chemical reactions when hydrogen cyanide (HCN) and sulfuric acid (H2SO4) are mixed with each other. In this study, we have covered a range of sulfuric acid concentrations (59-99 wt %) and HCN/H2SO4 mole ratios (0.25-15) and identified "hazardous zones" in these regions. Highly energetic reactions have been observed between hydrogen cyanide and sulfuric acid, with a 0.5-1 HCN/H2SO4 mole ratio in conjunction with 99 and 78.4 wt % H2SO4 being the worst-case scenarios. The test results have been fitted with a statistical model to generate contour plots that provide an overall perspective on the reaction severity. We have also investigated these reactions further by analyzing the reaction products and by using quantum mechanical calculations, the latter to determine the reaction pathways of least resistance. At least two sets of reactions have been noted between HCN and sulfuric acid, and the amount of water present in the system appears to wield marked influence on reaction pathways as well as their energies. Phosphoric acid, on the other hand, is far less reactive with HCN, and their mixtures appear to be stable over a broad temperature range. In light of the safety implications associated with HCN and sulfuric acid reactions, recommendations have been made to help raise awareness of, and to avoid, the potential dangers involved.