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 `K_p` for the given equilibrium ?
`2HI_((g)) hArr H_(2(g)) + I_(2(g))`

Explanation

`{:("Reaction:", 2HI_((g)) hArr, H_(2(g)) + , I_(2(g))),("Initial pressure:","0.2 atm",zero,zero),("Change in reaction :", "-2x atm","x atm","x atm"),("Partial pressure at equilibrium :", (0.2-2x), "x atm","x atm"),(,=0.04 "atm", =0.08 "atm" , =0.08 "atm"):}`
At equilibrium partial pressure of HI = 0.2 - 2x = 0.04
`therefore` 2x=0.2 - 0.04 =0.16
`therefore` x=0.08 atm
Thus, `p_(HI)`= 0.04 , `p_(H_2)` = 0.08 = `p_(I_2)`atm
`K_p=((p_(H_2))(p_(I_2)))/((p_(HI))^2)="(0.08 atm)(0.08 atm)"/"(0.04 atm)"^2=4.0`