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|Four glass tubes are sealed with NO2 gas. |
Compare the glass tubes.
NO2 is brown and N2O4 is colorless. The intensity of the brown color decreases as the temperature decreases. Therefore, a decrease in temperature yields and increase in N2O4. Equilibrium is shifted to the N2O4 side upon a decrease in temperature.
2 NO2 (g) <=> N2O4 (g)
The standard enthalpy (delta H° = -57.2 kJ) and the entropy (delta S° = -175.83 kJ) of reaction can be calculated from the follow standard-state enthalpies of formation and standard-state entropies.
|Compound||delta H°f (kJ/mol)||delta S° (J/mol-K)|
We can then invoke the assumption that the temperature dependence of delta H° for this reaction is small to estimate the equilibrium constant at various temperatures.
|Temperature||delta G° (kJ)||Kp|
|-78 °C||-22.9||1.3 x 106|
|-196 °C||-43.6||3.7 x 1029|