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Chemistry LibreTexts

Equilibrium of NO2/N2O4

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Required Training

Required PPE

UC Lab Safety Fundamentals

Lab coat, safety glasses/goggles,

nitrile gloves

Equipment

Chemicals

Sealed 250 mL bulbs of Nitrogen Dioxide

800 mL Beakers

Utility Clamps

Band Clamps to fit Beakers

Procedure:

Four glass tubes are sealed with NO2 gas

  1. The first tube is placed in a hot water bath
  2. The second in ice-water
  3. The third in flask with dry-ice/acetone
  4. 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/molK)

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: clipboard_e4b742660d4788e29a0053eb769095257.pngclipboard_ee200e352ff5c25914edc7a439fcf1444.png

Acutely Toxic – Nitrogen Dioxide

Corrosives – Nitrogen Dioxide


Equilibrium of NO2/N2O4 is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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