CHEMISTRY · Single correct · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
Phosgene is produced according to the equilibrium
CO(g)+Cl2(g)⇌COCl2(g).
A sample at equilibrium is contained in a rigid flask. Helium gas is then injected until the total pressure doubles, while the temperature remains constant. Which of the following best describes the system immediately after the helium is added and before any further reaction occurs?
(a) Because the total pressure has doubled, the partial pressures of all species also double, so Qp>Kp and the equilibrium shifts to the left.
(b) The equilibrium constant Kp decreases when pressure increases, causing the equilibrium to shift to the left.
(c) The partial pressures of the reacting gases remain unchanged, so Qp=Kp and the system is still at equilibrium.
(d) The increase in pressure favors the side with fewer moles of gas; therefore the equilibrium shifts to the right toward COCl2.