Consider the gas-phase equilibrium at 400 K:
PCl5(g)⇌PCl3(g)+Cl2(g),Kp=1.6
A 2.00 L rigid container at 400 K is charged with 0.200 mol of PCl5, 0.100 mol of PCl3, and 0.100 mol of Cl2 and allowed to come to equilibrium.
Starting from this equilibrium state, three separate containers experience the instantaneous volume changes described below; temperature is held constant and the time scale of the volume change is short enough that no reaction occurs during expansion or compression.
• Container X: The volume is doubled.
• Container Y: The volume is halved.
• Container Z: The volume is compressed to one-third its original value.
Assume ideal-gas behavior.
(a) Derive expressions for the partial pressures of all species immediately before the volume change in terms of the equilibrium extent of reaction, and determine their numerical values (in atm).
(b) For each container, compute the reaction quotient Qp immediately after the volume change.
(c) Rank the containers from the one that will experience the greatest net forward shift to the one that will experience the greatest net reverse shift in order to re-establish equilibrium.
(d) Justify your ranking in part (c) by discussing how the stoichiometry of the reaction influences the sensitivity of Qp to changes in total pressure.
(e) Predict qualitatively how the final total pressure in each container at the new equilibrium compares with the total pressure immediately after the volume change and explain your reasoning.