For the exothermic gaseous equilibrium 2 SO2(g) + O2(g) ⇌ 2 SO3(g) ΔH° = −198 kJ
CHEMISTRY · Single correct · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
For the exothermic gaseous equilibrium
2 SO2(g) + O2(g) ⇌ 2 SO3(g) ΔH° = −198 kJ,
a rigid 10.0-L container at constant temperature initially contains an equilibrium mixture. The system is then subjected to the following sequential stresses, re-equilibrating after each:
Step 1: The volume is compressed to 5.0 L while temperature is held constant.
Step 2: A small quantity of SO3 is quickly removed from the vessel.
After equilibrium is re-established following Step 2, the amount (in moles) of SO3 present in the container is, compared with the amount present in the original equilibrium mixture,
(a) approximately the same, because the compression shift is offset by the removal of SO₃.
(b) greater, because both stresses favor formation of SO3.
(c) indeterminate without numerical values for Kp and the initial partial pressures.
(d) smaller, because removing SO3 permanently lowers its amount in the vessel.