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

Question

Map The vapor pressure, P, of a certain liquid was measured at two temperatures, T. If you were going to graphically determine the enthalpy or vaporizaton,aHap, for this liquid, what points would you plot? The data is shown in this table. Number Number T (K) P (kPa) 325 3.46 675 8.57 To avoid rounding errors, use three significant figures in the x values and four significant figures in the y values 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? Number AHvap J/ mol

Explanation / Answer

we know that

the slope of the graph lnP vs 1/T can be used to obtain dHvap

so the x values will be 1/T and y values will be ln P

point 1 :

x = 1/325 = 0.00308

y = ln 3.46 = 1.241

point 2 :

x = 1/675 = 0.00148

y = ln 8.57 = 2.148

now

rise = y2 - y1 = 2.148 - 1.241 = 0.907

run = x2 - x1 = 0.00148 - 0.00308 = -0.0016

slope = rise / run = 0.907/ (-0.0016) = -566.875

now

we know that

slope = -dHvap / R = -566.875

dHvap = 566.875 x R = 566.875 x 8.314

dHvap = 4713 J /mol

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