The chemical equation for the thermal decomposition of ammonium dichromate is as follows:
(NH4)2Cr2O7 (s) = Cr2O3 (s) + N2 (g) + 4 H2O (g) (ΔH=−429 kcal/mol)
The reaction has been used in pyrotechnics, to demonstrate volcano experiment that involves igniting a pile of the salt, which initiates the above mentioned exothermic conversion.
Like the well-known explosive ammonium nitrate, it is thermodynamically unstable. Its decomposition reaction proceeds to completion once initiated, producing voluminous dark green powdered Chromium(III) oxide. Not all of the ammonium dichromate decomposes in this reaction. When the green powder is brought into water, a yellow/orange solution is obtained from left over ammonium dichromate.