When Phosphorus Pentachloride, PCl₅, Is Heated at a Constant Pressure

Multiple Choice

When phosphorus pentachloride, PCl₅, is heated at a constant pressure of exactly 1 bar to a temperature of 1400 K, the amount of phosphorus pentachloride decreases by 20.7% because of dissociation to phosphorus trichloride, PCl₃, and chlorine, Cl₂. Determine the equilibrium constant at this temperature.

A) 42.8  10^-3
B) 87.7
C) 0.207
D) 0.045