Clausius-Clapeyron Equation The variation of vapor pressure with temperature can

Question

Clausius-Clapeyron Equation The variation of vapor pressure with temperature can be expressed by the Clausius-Clapeyron Equation. The two-point form of this equation can be written as: ln p2 = Hvap 1 1 p1 R T2 T1 where p2 and p1 are the values of the vapor pressure at the Kelvin temperatures T2 and T1, respectively, Hvap is the molar heat of vaporization, and R is the ideal gas constant. Notice that p2 is over p1, there is a minus sign preceding Hvap/R, and T2 comes before T1. This is the form of the equation used in the OWL feedback. You may see slightly different, but equivalent forms, of this equation. It's easy to confuse the different forms. They will all give the same result, but not if you mix parts of one form with parts of another! Here are two forms that you are likely to see. Can you spot the differences between these and the OWL form above? ln p2 = Hvap 1 1 p1 R T1 T2 ln p1 = Hvap 1 1 p2 R T2 T1 Both of these are missing the minus sign preceding Hvap/R. In the first one, this is balanced by interchanging the 1/T2 and 1/T1 terms. In the second one, this is balanced by interchanging p2 and p1. The vapor pressure of liquid aluminum is 400 mm Hg at 2.59×103 K. Assuming that its molar heat of vaporization is constant at 296 kJ/mol, the vapor pressure of liquid Al is mm Hg at a temperature of 2.56×103 K.

Explanation / Answer

ln (P2/P1) =  Hvap/R [(1/T1) - (1/T2)]

Hvap = 296 kJ/mol

R = 0.0083 kJ/K.mol

T1 = 2.59*103 K = 2590 K

T2 = 2.56*103 K = 2560 K

P1 = 400 mm of Hg

P2 = ?

Putting these values in equation

ln (P2/400) = (296/0.0083) [(1/2590)-(1/2560)]

ln (P2/400) = 35662 [0.000386-0.000391]

ln (P2/400) = -0.1783

P2/400 = 0.837

P2 = 334.7 mm

Vapour pressure at temperature of 2560 K = 334.7 mm of Hg

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.