[rleung]

Hi,

I have a quick question.  It says that the vapor pressure of water at 80 degrees is 0.467 atm.  I need to find the value of Kc for the reaction: H2O(l) ---> H2O(g)

Does this problem have enough info for me to solve it?  Don't I need to know the volume it is contained in so that I can use PV=nRT to find the moles of water?  Thanks.

Ryan

[tamim83]

You can calculate the Kp for this reaction at 80 degrees Celsius.  The Kp expression is similar to the Kc expression, only you use partial pressures instead of concentrations.  Then you can convert the Kp to Kc using this equation:

Kp=Kc (RT)^{delta n}

Use R=8.314 J/mole * K and convert 80 degrees Celsius to Kelvin.  Delta n is equal to the sum of the coefiecents for gasseous products minus the sum of the coefficients for gaseous reactants.  In this case, delta n is just equal to one (no gaseous reactants).  As usual with heterogenous eqilibrium, you can ignore the partial pressure/concentration of the liquid water since both will be larger than one. 

Good Luck, hope this helps. 

[rleung]

Ah, I see now!  I feel so stupid forgetting that equation.  But thanks so much...you were a great help

Ryan

[tamim83]

No Problem, glad to help out