Equilibrium of NO2/N2O4
- Page ID
- 128810
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Required Training |
Required PPE |
|---|---|
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UC Lab Safety Fundamentals |
Lab coat, safety glasses/goggles, nitrile gloves |
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Equipment |
Chemicals |
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Sealed 250 mL bulbs of Nitrogen Dioxide |
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800 mL Beakers |
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Utility Clamps |
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Band Clamps to fit Beakers |
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Procedure:
Four glass tubes are sealed with NO2 gas
- The first tube is placed in a hot water bath
- The second in ice-water
- The third in flask with dry-ice/acetone
- The fourth in liquid nitrogen
NO2 is brown and N2O4 is colorless. The intensity of the brown color decreases as the temperature decreases. Therefore, a decrease in temperature yields an increase in N2O4. Equilibrium is shifted to the N2O4 side upon a decrease in temperature.
Discussion:
Brown 2 NO2 (g) ⇌ N2O4 (g) Colorless
The standard enthalpy (∆Hrxn = -57.2 kJ) and the entropy (∆Srxn = -175.83 J) of reaction can be calculated from the following standard-state enthalpies of formation and standard-state entropies:
|
Compound |
∆Hf (kJ/mol) |
∆S (J/mol•K) |
|---|---|---|
|
NO2 |
33.18 |
240.06 |
|
N2O4 |
9.16 |
304.29 |
We can then use the assumption that the temperature dependence of ∆H for this reaction is small to estimate the equilibrium constant at various temperatures.
|
Temperature |
∆G (kJ) |
Kp |
|---|---|---|
|
100 ⁰C |
8.4 |
0.066 |
|
0 ⁰C |
-9.2 |
58 |
|
-78 ⁰C |
-22.9 |
1.3x106 |
|
-196 ⁰C |
-43.6 |
3.7x1029 |
Hazards:
Nitrogen Dioxide is a corrosive and poisonous gas; use caution when handling the glass tubes.
SOP: 
Acutely Toxic – Nitrogen Dioxide
Corrosives – Nitrogen Dioxide