A reaction mixture initially contains 0.50 mol of gaseous E and 0.50 mol of gaseous F…
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
A reaction mixture initially contains 0.50 mol of gaseous E and 0.50 mol of gaseous F in a rigid 2.0 L container at 600 K. The gases react according to the equation E + F ⇌ G (only one mole of product is formed per mole of each reactant).
A researcher continuously records the partial pressures of E, F, and G. The following verbal description summarizes the data:
• From 0 min to 8 min, PE and PF decrease rapidly while PG increases.
• From 8 min to 12 min, all three partial pressures remain constant within the precision of the instrument.
• At 12 min the temperature is suddenly lowered to 550 K; the volume does not change.
• Immediately after the temperature drop, PG begins to decrease while PE and PF increase until they again reach constant values at 20 min.
(1) Identify the two distinct time intervals during which the system is at equilibrium, and state the evidence that supports your identification for each interval.
(2) Explain why the partial pressures change in the direction observed immediately after the temperature is lowered at 12 min.
(3) Sketch qualitative curves of the forward and reverse reaction rates versus time for the entire 0 – 20 min interval. Clearly label the times corresponding to the temperature change and to each equilibrium period.
(4) Suppose the volume of the container were doubled at 8 min instead of changing the temperature at 12 min. Predict qualitatively how the partial pressures of E, F, and G would respond immediately and over time, and justify your predictions.