E715: Prep Notes

Introduction

Sealed tubes of a pale brown mixture of NO2 and N2O4 are placed in hot and cold baths to shift the equilibrium.  The coloration of the gas inside shows the effects.

Equations

2NO2(g)     ↔    N2O4(g) + Δ

brown               colorless 

Supplies

Short List

  •  one tall 1000mL beaker with hot water and  a tray of dry ice 
  •  hot plate
  •  heat protected glove

Chemicals

  • two or three sealed tubes of NO2/N2O4
  • two tall 1000mL beakers, one with hot water and one with ice water  

Prior to Lecture  

1.     Prepare the following solutions:

  •  one tall 1000mL beaker with hot water and  a tray of dry ice 
  •  hot plate
  •  heat protected glove
  • two or three sealed tubes of NO2/N2O4
  • two tall 1000mL beakers, one with hot water and one with ice water  

To Conduct Demonstration:  

  1. Place one tube in the cold bath.  The equilibrium will shift toward N2O4 and the tube will lose color intensity.
  2. Place one tube in the hot bath.  The equilibrium will shift toward NO2 and the color intensity will increase.

Safety and Disposal

NO2 is a toxic gas.  In case the tubes break, do not breathe escaping gas.  Wear heat-protective gloves when handling very cold or very hot tubes.