# [SOLVED] Heat sublimation ? not in my book or anywhere online

Heat sublimation ? not in my book or anywhere online

The standard heat of formation of PI3 (s) is -24.7 and the bond energy in this PI molecule is 184 . The standard heat of formation of P (g) is 334 and that of I2 (g) is 62 . The I2 bond energy is 151 .

Calculate the heat of sublimation of .

PI3 [PI3(s) –> PI3 (g) ]

not even in my book or not talked about in class but somehow is given as a hw problem go figure

This is the best answer for Heat sublimation?

_____I answered this Q before. You said I was wrong; maybe you can tell me why. Did you use the sum of the eqns? I did and they do give the right answer. If you use the ~value I supplied, that was about right, then you got the wrong answer; I expected you to do the math. I also gave a ref of what the answer should be; (the sum of the dHs just might NOT give that number within 1%!

to 1st approximation: heat sublimation of PI3 ~ (MW PI3 / MW I2) * heat sublimation of I2.

I have given the answer below, again.

_____Bond energy and enthalpy combination and HESS

_____1/4P4(s)—————–> P(g)_______dHvap = 334 kJ/mole P

___3/2 * [I2(s) ——————> I2 (g)]_____dHvap = 3/2 * 62 kJ/mole I2

_____P(g) +3/2 I2(g)———> PI3(g)____dHrxn= – [(3 bonds*184) – 3/2 bonds*151]kJ/mole

sum eqns and dHs above

_____1/4P4(s) + 3/2 I2(s) —> PI3(g)_____dHf PI3(g) = sum dHs = ?? kj/mole

_____PI3(s) ——–> 1/4P4(s) + 3/2 I2(s)__-dHf PI3(s) = 24.7 kJ/mole

sum eqns and dHs for these two reactions

_____PI3(s) ——————–> PI3 (g) ___________dHsubl = ??

SOLVE (answer should be ~ 95 kJ/mole; not ~400 kJ/mole)

Basic mathematics is a prerequisite to chemistry – I just try to help you with the methodology of solving the problem.

22 hours ago

Source(s):

0.98 eV heat of sublimation of PI3 = 94.56 kJ/mole

1 eV = 96.48530891 kJ / mole (wikipedia)

Do the thought experiment: