7.11 A sample of HI(g) is placed in flask at a pressure of 0.2 atm. At equilibrium the partial pressure of HI(g) is 0.04 atm. What is Kp for the given equilibrium ?

2HI (g) H2 (g) + I2 (g)

The initial concentration of HI is 0.2 atm. At equilibrium, it has a partial pressure of 0.04 atm. Therefore, a decrease in the pressure of HI is 0.2 –

0.04 = 0.16. The given reaction is:    

2HIgH2g+I2g
Initialconc.0.2atm00
Atequilibrium0.04atm0.1620.162
=0.08atm=0.08atm
Therefore,
Kp=pH2×pI2p2HI
=0.08×0.080.042
=0.00640.0016
=4.0

Hence, the value of Kp for the given equilibrium is 4.0.