Phosphorus pentachloride dissociates in the gas phase,
PHYSICS · Multi-part · Fermi University Physics · Thermal, Statistical & Complex Systems · Thermodynamic potentials and the formal structure of thermodynamics · Thermodynamic potentials and the formal structure of thermodynamics
Thermal Physics, Ch Chemical potential, open systems and chemical equilibrium
Problem
Phosphorus pentachloride dissociates in the gas phase, PCl5⇌PCl3+Cl2. At 500K the tabulated standard Gibbs energy change for the reaction as written is ΔG∘=+6.4kJmol−1, referred to the standard pressure p∘=1bar. All three species are treated as ideal gases and the mixture as an ideal gas mixture. A vessel is filled with pure PCl5 and held at 500K until equilibrium is reached, the total pressure being held fixed. Let α be the degree of dissociation, the fraction of the original PCl5 that has decomposed.
((a)) Calculate the equilibrium constant K at 500K.
((b)) Find α when the total pressure is held at 1.5bar.
((c)) Find α when the total pressure is held at 3.0bar instead, and say in one sentence which way the extra pressure has pushed the reaction.