A sealed reaction vessel at 425 K contains the equilibrium mixture for 2…
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
A sealed reaction vessel at 425 K contains the equilibrium mixture for
2SO2(g)+O2(g)⇌2SO3(g)ΔH∘=−197kJmol−1
Assume the initial volume is 5.00 L and the total pressure is 2.00atm. Three separate experiments are performed, each starting from identical equilibrium conditions.
• Experiment 1: The volume is reduced to 2.50 L at constant temperature.
• Experiment 2: Helium is injected until the total pressure again reads 2.00atm; temperature and volume are held constant.
• Experiment 3: The temperature is raised to 475 K; volume is unchanged.
(1) Rank the three experiments and an untouched control (Experiment 0) from greatest to least final amount (in moles) of SO3 present after re-equilibration.
(2) For each experiment, construct a qualitative argument—based solely on changes to partial pressures, total moles of gas, or energetic favorability—that supports the ranking you produced.
(3) Explain why Experiments 1 and 2, despite involving similar changes in total pressure, do not produce the same shift in equilibrium.