Look up the vapor pressure of water at 25 C and look up its enthalpy of vaporiza
ID: 497570 • Letter: L
Question
Look up the vapor pressure of water at 25 C and look up its enthalpy of vaporization. Using the Clausius-Clapeyron equation, estimate the vapor pressure of water at 75 C in Torr. Now look up the measured vapor pressure at 75 C. How good is your estimate? List the approximations that you made to make the estimate. Vapor pressures are often tabulated according to the Antoine equation. For water, the equation is log_10 P = 5.08 - (1660/(T - 45.6)) between 344 and 373 K, where P is in bar and T is in Kelvin. Calculate the enthalpy of vaporization in kJ/mol in this temperature range from this equation, assuming it is constant.Explanation / Answer
Vapor pressure of water at 25 deg.c = 23.8 Torr. Let this temperature be T1
T1= 25+273= 298K, P1= 23.8 Torr
Latent heat of vaporization of water = 40.8 Kj/mole
T2= 75 +273= 348 K
From
Ln(P2/P1) =(deltaH/R)*(1/T1-1/T2)
Where deltaH= Latent heat of vaporization
Ln(P2/23.8)= (40.8*1000/8.314)*(1/298-1/348)
P2= 253.5 Torr
Literature value is =289.1 Torr
The estimate is based on
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