The vapor pressure, P, of a certain liquid was measured at two temperatures, T.

Question

The vapor pressure, P, of a certain liquid was measured at two temperatures, T. If you were going to graphically determine the enthalpy of vaporizaton, Hap, for this liquid, what points would you plot? The data is shown in this table Number Number T (K) P (kPa) 225 825 7.52 To avoid rounding errors, use three significant tigures in the x values and four significant figures in the y values 3.84 point 1 Number Number NOTE: Keep the pressure units in kPa point 2 Determine the rise, run, and slope of the line formed by these points rise run slope Number Number Number What is the enthalpy of vaporization of this liquid? Numbe J/ mol vap

Explanation / Answer

We need to plot lnK on y axis and 1/T on x axis
P = 3.84
ln P = ln (3.84) = 1.34547
T = 225.0
1/T = 0.00444


point 1 is:
x = 0.00444
y = 1.34547


P = 7.52
ln P = ln (7.52) = 2.01757
T = 825.0
1/T = 0.00121


point 2 is:
x = 0.00121
y = 2.01757


----------------------------------------------------------------------------
rise = (y1-y2) = 1.34547 - 2.01757 = -0.67209
rise = (X1-X2) = 0.00444 - 0.00121 = 0.00323
slope = rise/run
= -0.67209/0.00323
= -207.92901
----------------------------------------------------------------------------
use
slope = - delta H/R
= -207.92901 = -delta H/8.314
delta H = 1729 J/mol

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