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

Question

The vapor pressure, P, of a certain liquid was measured at two temperatures, If you were going to graphically determine the enthalpy of vaporizaton, AHap, for this liquid, what points would you plot? The data is shown in this table. Number Number T (K) P(kPa) 275 3.46 525 5.55 point 1 To avoid rounding the x and four Number Number NOTE: Keep the pressure units in kPa. the y vaiues. point 2: Determine the rise, run, and slope of the line formed by these points. run slope rise Number Number What is the enthalpy of vaporization of this liquid? Number J/ mol vap Hint

Explanation / Answer

We need to plot lnK on y axis and 1/T on x axis
P = 3.46
ln P = ln (3.46) = 1.24127
T = 275.0
1/T = 0.00364


point 1 is:
x = 0.00364
y = 1.24127


P = 5.55
ln P = ln (5.55) = 1.7138
T = 525.0
1/T = 0.0019


point 2 is:
x = 0.0019
y = 1.7138


----------------------------------------------------------------------------
rise = (y1-y2) = 1.24127 - 1.7138 = -0.47253
rise = (X1-X2) = 0.00364 - 0.0019 = 0.00173
slope = rise/run
= -0.47253/0.00173
= -272.88569
----------------------------------------------------------------------------
use
slope = - Hvap/R
= -272.88569 = -Hvap/8.314
Hvap = 2269 J/mol
Answer: 2269 J/mol

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