Hello

I’m solving previous exams and there is this exercise that appears in almost every exam :

I’m solving previous exams and there is this exercise that appears in almost every exam :

**1. The problem statement, all variables and given/known data**Suppose v moles of a gas H2O are enclosed in a constant volume V at a low temperature so the gas is in aN undissociated state. At highest temperatureS, H2O molecules are dissociated

2H2O-> 2H2 + O2

If "f" is the fraction of H2O molecules that are dissociated at a known temperature T, and p the total pressure of the gas at that temperature, show that Kp(T) at this pressure is :

Kp(T)= p f^3/ (( 1-f)^2(2+f) )

**2. Relevant equations**

**3. The attempt at a solution**

Kp(T)= (P_{H20}/p)²/ [ (P_{02}/p)*(P_{H2}/p)² ]

= p*P_{H20}²/ [ P_{02}*P_{H2}² ]

And then I dont know how to get to the given expression :confused:

http://ift.tt/1jG2X0I