is stable to air. It is, however, unstable in the thermodynamic sense with a positive enthalpy of formation of +460 kJ/mol. This endothermic enthalpy of formation originates in the difference in energy of  compared to its highly stable decomposition products:
Because one of its decomposition products is a gas,  can be used as an explosive. Purer samples tend to be more explosive. Small samples can be detonated by striking with a hammer.  is thermochromic, changing from pale yellow below −30 °C to orange at room temperature to deep red above 100 °C.