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

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. 

Acknowledgment 

Adelaide Dittmar, Spring 1986; Stewart Strickler, Fall 1995.