Question

For the reaction equilibrium, 2NOBr (g) 2NO (g) + Br2 (g), If PBr2 = P/9 at equilibrium and P is total pressure. The ratio Kp/P is equal to:<br />..Why please explain..?why P/3 is being used

Answer 1

expression for Kp for the given reaction= Kp= P no² x P br2/ Pnobr

Given:  in the equilibrium conditions the partial pressure of 2NO will be two times more then the partial pressure of Br2

so,  partial pressure of 2NO= 2 x P/9

total pressure= P

The partial pressure of 2NOBr in the equilibrium conditions will be 2NOBr
= P – 2 x P/9 – P/9
= 6 x P/9
= 2 x P/3  

 constant of equilibrium, Kp: 

Kp= P no² x P br2/ Pnobr
= (2 x P/9)² x P/ 9 /(2 x P/3)²
= 4 x P³/729 divide 4 x P²/9
= P/ 81

 Kp/P will be: 

= P/81 divide P
= 1/81