Chemical Concepts Demonstrated

• Complex stoichiometry
• Exothermicity

Demonstration

A tube filled with NO gas is sealed with a rubber stopper. CS2 is quickly added to the tube (the demonstrator is careful not to allow any air to be admitted, since NO reacts with oxygen to form NO2). The tube is inverted to insure complete mixing. The rubber stopper is then removed, and a lighted match is thrown down the tube.

Observations

As the match travels down the tube, a massive flame and a loud roar shoot forth from the top of the tube.

Explanation (include important chemical equations)

The reaction witnessed involves a very complex stoichiometry:

5 CS₂ + 10.8 NO -> 5.4 N₂ + 2.6 CO + 2.4 CO₂ +1.7 SO₂ + 8.3 S

The reaction is first-order in CS₂ and second-order in NO.  The activation energy is 300 kJ/mol, which is the energy required to remove an S from CS₂.  The energy released in this reaction is a whopping 3,280 kJ/mol.

Contributors

• Dr. George Bodner (Perdue University)