1)The following information is given for water , H 2 O , at 1atm: At a pressure
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Question
1)The following information is given for water, H2O, at 1atm:
At a pressure of 1 atm, kJ of heat are needed to vaporize a 26.0 g sample of liquid water at its normal boiling point of 100 °C.
2)The following information is given for ethanol, C2H5OH, at 1atm:
At a pressure of 1 atm, kJ of heat are needed to vaporize a 47.9 g sample of liquid ethanol at its normal boiling point of 78.4 °C.
3)The vapor pressure of liquid bismuth is 400 mm Hg at 1.72×103 K. Assuming that its molar heat of vaporization is constant at 149kJ/mol, the vapor pressure of liquid Bi is mm Hg at a temperature of 1.76×103 K.
boiling point = 100 °C Hvap(100 °C) = 40.7 kJ/mol specific heat liquid = 4.18 J/g°CExplanation / Answer
Moles of water= mass of water/molar mass= 26/18=1.44
Liquid water changes its phase from liquid water to water vapor at 100 deg.c by the supply of latent heat of VaporizationHeat to be added = moles of water* latent heat of vaporization
Moles of water= mass of water/ molar mass= 26/18 =1.44 mole
Heat to be added= moles of water* molala heat of vaporization = 1.44 moles*40.7KJ/mole =56.1 KJ
2.
Moles of ethanol= mass of water/molar mass= 47.9/46=1.041
Liquid ethanol changes its phase from liquid to vapor at 78.4 deg.c by the supply of latent heat of Vaporization
Heat to be added = moles of water* latent heat of vaporization
Heat to be added= moles of ethanol* molala heat of vaporization = 1.041moles*38.6KJ/mole =40.2KJ
3. Classius-Clayperon Equation will be used to determine the vapor pressure (P2) at temperature (T2, in K) provided the vapor pressure P1 at temperature T1 is known and alos the latent heat of vaporization
Theequation is ln ln(P2/P1)= (deltah/R)*(1/T1-1/T2)
given T1= 1.72*1000K P1= 400mm Hg, T2= 1.76*1000K, deltaH= 149 KJ/mole, = 149 Kj/mol*1000J/kj= 149000 J/mole, R= 8.314 J/mole.K
hence ln(P2/P1)= (149*1000/8.314)*(`1720-1/1760)
P2= 507 mm Hg. The assumptions that is made is that latent heat does not change with temperature
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