CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
Nitrogen dioxide, NO2 (brown gas), and dinitrogen tetroxide, N2O4 (colorless gas), interconvert in a rigid, sealed glass tube according to the reversible reaction
N2O4(g) ⇌ 2 NO2(g)
At 25 °C the system is at equilibrium and appears a light brown color.
The tube is then placed in a 40 °C water bath. Assume the temperature increase is rapid compared with the time required for the system to re-establish equilibrium and that the volume of the tube remains constant throughout the experiment.
(a) Immediately after the temperature is raised (before any appreciable composition change has occurred), describe how the forward and reverse reaction rates compare to one another. Justify your answer in terms of how temperature affects molecular collisions and reaction rate constants.
(b) Identify the direction of the net conversion (toward NO2 or toward N2O4) during the period when the system is adjusting to the new temperature. Explain your reasoning by referring explicitly to the relative magnitudes of the two opposing rates.
(c) Describe qualitatively how the relative rates will change as the composition of the gas mixture evolves toward the new equilibrium. State the condition that will eventually be re-established once equilibrium at 40 °C is reached.