[ideedit]

Hi everyone,

Need some help with this p. chem problem. Here it is:

Close to the triple point (T=273K), the vapor pressure of ice is given by the following equation:
ln(P)=-(5924/T)+2.71*ln(T)-0.0072T+9.812
where P and T are expressed in torr and K. Calculate the molar enthalpy of sublimation, fusion, and vaporization, and the change in the molar volume during fusion.

So far:
I know dHsub=dHfus+dHvap.
I know that I am going to be using the clausius clapeyron eqn and I used it in the form of
lnP=-dHsub/RT + K = -a/RT + ln(T)*(b/R) + T*(c/R) + K       (1)
plugged the given equation for vapor pressure into the right hand side of (1) and solved for dHsub (=19.04kJ/mol).

I don't know where to go from here, or if I solved for dHsub correctly.

Thanks!

[Enthalpy]

19kJ/mol are too little to my taste. You got 1MJ/kg for sublimation near 0°C but vaporization near 100°C is already 2.25MJ/kg.

As for the method, I too would write that P varies as exp(-H/RT), yes. Beware the natural logarithm, and consistent units at H R T (cal vs J, mol vs kg, K vs F...). Don't forget to differentiate all terms in the Ln(P) expression.

Fusion and vaporization: is that serious? Or are you supposed to inject other known values?

As the triple point is a point, "near" it can only mean ice-vapour equilibrium without any liquid, and below 0°C. Where is there information about a liquid in this expression?

[ideedit]

i know... there is no information about vapor pressure of liquid in the problem statement. that's what is confusing me.

i really don't understand how i should go about this problem. i thought i had dHsub calculated correctly. if i can find Hsub and either Hvap or Hfus, i can use Hsub=Hvap+Hfus to find the last. but i don't know which to start with..

any help is appreciated!