a) Assume that the H o and S o of vaporization do not change significantly with
ID: 962569 • Letter: A
Question
a) Assume that the Ho and So of vaporization do not change significantly with temperature. Calculate the vapor pressure of CH3OH at 50 oC (in atm).
CH3OH (l) CH3OH(g) . . . Ho = 38.0 kJ and So = 112.9 J/K
(Don't round until the end. Using the exponent enlarges any round-off error.)
b) Calculate the vapor pressure of Hg at 25 oC (in atm).
Hg(l) Hg(g) . . . Ho = 61.32 kJ and So = 98.83 J/K
c) Calculate the average C—C bond strength in cyclopropane (in kJ/mol). Its combustion and the experimental enthalpy of reaction are:
C3H6(g) + 4.5O2(g) 3CO2(g) + 3H2O(g) Hºrxn = -1,957.7 kJ/mol
Explanation / Answer
a)
Apply Clasius equation
ln(P2/P1)= H/R*(1/T1-1/T2)
normal Bp = 64.7 at P = 1 atm so
ln(P2/1)= 38000/8.314*(1/(64.7+273) -1/(50+273))
P2 = exp(38000/8.314*(1/(64.7+273) -1/(50+273)))
P2 = 0.54011 atm
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