Chemical Concept Demonstrated: Temperature's effect on equilibrium
|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.
Explanation (including important chemical equations):
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|