Chemical Concepts Demonstrated

• Explosive exothermic reactions
• Shock sensitive substances
• Compounds that decompose into their elements

Demonstration

Behind a safety shield, dry NI₃ is "provoked" using a feather.

Observations

A violent explosion occurs.

Explanation (including important chemical equations)

NI₃ is very unstable and detonates upon provocation:

2 NI₃ -> N₂ + 3 I₂

Nitrogen triiodide has an enthalpy of formation of 154.4 kJ/mol.   As a result, the reaction in which it decomposes to form its elements is favored by both enthalpy and entropy.

It should be noted that this can be a very dangerous demonstration if safety precautions are not strictly followed.  Many people have been injured, some seriously, while doing this demonstration.  Only small amounts of nitrogen triiodide should be made at any given time, and the substance should never be stored.  This substance can only be moved while still damp from its formation, and should be kept away from heat, sunlight, and anyone who doesn't know the inherent danger involved in the demonstration.

Contributors 

• Dr. George Bodner (Perdue University)