4.5 moles each of hydrogen and iodine were heated in a sealed ten litre vessel. At equilibrium 3 moles of HI were found. The equilibrium constant of H2(g)+I2(g)⇌2HI(g) is

H2+I2⇌2HI Initial moles      4.5       4.5       0Moles at eqm   3          3          3K=(3)23×3=1 .Note : when there is no change in the number of moles, Δn=0 the volume or capacity of vessel can be ignored.