A rigid 2.0 L vessel contains the equilibrium mixture for the gaseous reaction…
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
A rigid 2.0 L vessel contains the equilibrium mixture for the gaseous reaction
PCl5(g)⇌PCl3(g)+Cl2(g)
The total pressure inside the vessel is monitored with a pressure probe and recorded as a function of time. The probe produces the following trace:
• From t = 0 s to t = 120 s, the total pressure remains constant at 1.0 atm.
• At t = 120 s the total pressure drops instantaneously to 0.50 atm.
• Over the next several minutes the pressure rises gradually and levels off at a new steady value of 0.65 atm.
Assume temperature remains constant throughout.
(1) Propose the specific physical change made to the system at t = 120 s that produced the pressure trace described above.
(2) Explain quantitatively or qualitatively why the total pressure first decreased abruptly and then increased to the new steady value.
(3) Predict whether the final partial pressure of PCl₅ is greater than, less than, or equal to its initial value. Support your prediction.
(4) State whether the numerical value of Kp for the reaction changed as a result of the disturbance. Justify your answer.