Stock Video - Ammonium dichromate volcano demonstration. Ammonium dichromate is a salt that decomposes in an exothermic reaction when ignited. The decomposition produces a large volume of dark green chromium (III) oxide, along with steam and nitrogen gas. The equation for the reaction is: (NH4)2Cr2O7 --> Cr2O3 + N2 + 4H2O. This clip is also available with the chemical equation for the reaction overlaid. See clip K004 3413.