Chemical Equilibrium: N₂O₄ (Colorless) ⇌ 2 NO₂ (Dark Red-Brown)

Investigate dynamic equilibrium, van 't Hoff temperature dependence, and Le Chatelier 's principle under volume and temperature perturbations with live optical gas density transmittance.

Equilibrium Kc0.0059 M

Reaction Pressure7.2 atm

Sealed Piston Gas Reaction Vessel

ΔH° = +57.2 kJ/mol (Endothermic)

PISTON (V = 2.0 L)

[N₂O₄] = 0.2556 mol/L

[NO₂] = 0.0388 mol/L

Optical Absorbance: A = 0.33

⬅️ Le Chatelier: Reverse Shift (Forming Colorless N₂O₄)

Reaction Vessel Controls

Temperature (T):298 K (25 °C)

Endothermic reaction: Heating increases Kc, shifting equilibrium to dark brown NO₂.

Vessel Volume (V):2.0 Liters

Compression increases pressure: Le Chatelier shifts equilibrium toward fewer gas moles (N₂O₄).

Mathematical Equilibrium Principles

Equilibrium Constant:

K_c = \frac{[\text{NO}_2]^2}{[\text{N}_2\text{O}_4]}, \quad Q_c = \frac{c_{\text{NO}_2}^2}{c_{\text{N}_2\text{O}_4}}

Van 't Hoff Equation:

\ln\left(\frac{K_2}{K_1}\right) = -\frac{\Delta H^\circ}{R}\left(\frac{1}{T_2} - \frac{1}{T_1}\right)