A closed 1.00 L vessel at 298 K contains the gaseous equilibrium
NO2 (g) ⇌ N2O4 (g)
with initial partial pressures of 0.200 atm NO2 and 0.000 atm N2O4. After several minutes the system becomes pale yellow, indicating that equilibrium has been established.
A chemist then injects a finely divided solid that is known to catalyze the dimerization of NO2. The total volume, temperature, and total pressure of the vessel remain unchanged.
Answer the following questions. Provide clear chemical reasoning throughout your response.
(a) Describe qualitatively how the presence of the catalyst alters (i) the forward rate of NO2 dimerization and (ii) the reverse rate of N2O4 dissociation.
(b) Predict whether the equilibrium partial pressures of NO2 and N2O4 will change after the catalyst is added. Justify your prediction in terms of kinetic and thermodynamic arguments.
(c) The chemist observes that the colour of the mixture fades to an even paler yellow more rapidly after the catalyst is added. Explain why this observation is consistent with your answer to part (b).
(d) Identify one experimental measurement, other than colour, that could be monitored in real time to verify the catalyst’s effect on the *rate* without affecting the *position* of equilibrium. Explain how the data would support your conclusion.