Ammonium Dichromate is a somewhat compact orange solid that when heated decomposes into a green solid Chromium(III)Oxide( that appears to grow in size) along with nitrogen and stream. You can see why this reaction is called a volcano reaction.
The reaction
(NH4)2Cr2O7 (s) → Cr2O3 (s) + N2 (g) + 4 H2O (g) (ΔH=−429.1 ± 3 kcal/mol)
