Decomposition of Ammonium Dichromate: Chemical Reactions and Demonstrations
When ammonium dichromate, represented by its chemical formula NH_4_2Cr_2O_7, is heated strongly, it undergoes a decomposition reaction. This process results in the formation of chromium(III) oxide, nitrogen gas, and water vapor, along with other products.
Chemical Equation and Balanced Reaction
The balanced chemical equation for the decomposition of ammonium dichromate is as follows:
2NH42Cr2O7(s) → Cr2O3(s) N2(g) 4H2O(g)
This reaction is notable for its vivid color change and the release of gases, often making it a favorite demonstration in chemistry experiments.
Common Science Demonstration: The Dichromate Volcano
The heating of ammonium dichromate is the basis for a well-known chemistry demonstration called the Dichromate Volcano. When a bright orange pile of the solid is ignited, the reaction produces nitrogen gas, water as steam, and chromium trioxide (green in color).
The dramatic color change is due to the formation of chromium trioxide, which expands in volume due to the embedded gases. As a result, the pile appears to grow. The reaction is strongly exothermic and can occur in a sealed container, potentially leading to an explosion. A notable case is the Diamond Shamrock Chemicals incident in Ashtabula, Ohio, in 1986, where an explosion occurred due to similar reactions.
Auto-Redox Reaction
The decomposition of ammonium dichromate can also be classified as an auto-redox reaction, similar to the decomposition of ammonium nitrate. The balanced chemical equation is:
4NH42 CrO4-2 → 2Cr2O3 2N2 8H2O O2
Both of these reactions involve the oxidation and reduction of chromium and the decomposition of nitrate and dichromate ions.
Understanding and observing these chemical reactions are vital for chemistry students and educators. This decomposition process not only provides a visually stunning demonstration but also offers insights into the principles of chemical reactions, redox processes, and exothermic reactions.
For further exploration, one may refer to books on inorganic chemistry, laboratory manuals, and online resources that provide detailed information on these chemical processes.