Explosive Decomposition

1. Explosive Decomposition When a substance is touched at length it explodes with a loud bang

2. Purpose • To observe an explosive decomposition reaction • To understand the reason the substance is explosive

3. Demonstration • Because the iodine atoms repel each other the molecule was unstable and detonated with the slightest vibration • The chemical equation for the chemical reaction was 8 NH3 NI3 5 N2 + 6 NH4I +9 I2

4. Concepts 1. Decomposition Reactions 2. Atomic Size 3. Redox Reactions

5. 1. Decomposition Reactions • General Form is AB A + B The substance AB has broken apart into two new substances, A and B • In this demonstration AB is the substance nitrogen triiodide, NI3

6. 2. Atomic Size (I) • Atoms are spherical but have different sizes • The relative sizes can be predicted from Periodic Trends on the Periodic Table Slight decrease in size for most part Period (horizontal row) Group (vertical row) Large increase

7. Atomic Size (II) • The substance in this demonstration is nitrogen triiodide, NI3 • The relative size of atomic radii are Nitrogen 0.75 Iodine 1.32 • The molecule therefore looks like this • Bulky iodine atoms surround • the smaller nitrogen atom • Iodine electrons repel each other • making the molecule unstable

8. 3. Redox Reactions • In a redox reaction, one substance loses electrons while another substance gains electrons • “Redox” is a conventional term which is a combination of the words “reduction” AND “oxidation” • In this demonstration iodide is oxidized and nitrogen is reduced

9. Conclusions • Nitrogen triiodide was a very unstable compound which underwent a violent decomposition reactions • A knowledge of molecular structure was useful in understanding why nitrogen triiodide was explosive

10. Comments • Nitrogen iodide was first made in 1813 • Many seriously dangerous accidents have occurred when this and similarly unstable substances have detonated