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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: Collegekid on November 30, 2005, 08:58:52 PM

Title: Calculate ?U, ?A, ?G..
Post by: Collegekid on November 30, 2005, 08:58:52 PM

Two moles of water are allowed to vaporize at 100°C and 1 atm pressure.  The heat of vaporization of water at this pressure and temperature is 540 cal/g.  Calculate ?U, ?A, ?G, w, q, ?H, and ?S for this process in units of calories.  (This is just an example problem that I didn't know how to do.)

Title: Re:Calculate ?U, ?A, ?G..
Post by: mike on November 30, 2005, 09:01:24 PM

What have you done so far?

Did you search this site? This might help a little:

http://www.chemicalforums.com/index.php?board=6;action=display;threadid=5471

Title: Re:Calculate ?U, ?A, ?G..
Post by: Donaldson Tan on December 01, 2005, 04:02:50 PM

consider boiling water as an open system,

dH = Q + W = Q + VdP
Constant Pressure (dP=0): dH = Q

H = U + PV
Constant Pressure: dH = dU + PdV

Since at 100C, 1atm, water is at equilibrium, then
 ?S = Q/T

Mike's link will give you a clue on the value of dG.

To find ?A, try differentiating the expression for A