Equilibrium of NO₂ and N₂O₄

Materials

• Two sealed NO₂ (gas) equilibrium tubes
• 4 liter beaker of ice water
• 4 liter beaker of hot water
• Hotplate

Procedure

1. Place one tube in an ice bath and place a lid on top.
2. Use one tube as room temperature standard.
3. Place a third tube in a hot water bath and place a lid on top.
4. After a few minutes compare the color in the tubes.

Discussion:

Heat shifts the equilibrium in favor of NO₂ and the tube becomes darker. Since the formation of N₂O₄ is an exothermic reaction, lowering the temperature shifts the equilibrium in favor of colorless N₂O₄. In a dry ice - acetone bath, the N₂O₄ will crystallizes as a white solid.

\( \ce{ 2NO2 <=> N2O2 ~~~~ \Delta G_{rxn}^{{o}} = -2.8KJ/Mol } \)