- 16 - Sample Exercise 15.11 A 1.000-L flask is filled with 1.000 mol of H2 and 2.000 mol of I2 at 448o C. The value of the equilibrium constant, Keq , for the reaction H2(g) I2(g) ⇋ 2 HI(g) at 448o C is 50.5. What are the partial pressures of H2 , I2 , and HI in the flask at equilibrium? (P H2 = 3.9 atm, P I2 = 63.1 atm, P HI = 110.6 atm) Practice Exercise 15.11 For the equilibrium, PCl 5(g) ⇋ PCl3(g) Cl2(g), the equilibrium constant, Keq , has the value 0.497 at 500 K. A gas cylinder at 500 K is charged with PCl5(g) at an initial pressure of 1.66 atm. What are the equilibrium pressures of PCl5 , PCl3, and Cl2 at this temperature?