5/5/2016 5/3/2016 PM Gradebook Print Calculator Periodic Table Question 6 of 24

Question

5/5/2016 5/3/2016 PM Gradebook Print Calculator Periodic Table Question 6 of 24 pling earning The vapor pressure, P, of a certain liquid If you were going to graphically determine the enthalpy of was measured at two temperatures, vaporizaton, AHvap, for this liquid, what points would you plot? The data is shown in this table. Number Number T (K) P (kPa) To avoid rounding point 1: 325 3.35 errors, use three significant figures in 625 849 the X values and four Number Number significant figures in NOTE: Keep the pressure units inkPa. the y values. point 2: Determine the rise, run, and slope of the line formed by these points. slope rise run Number Number Number What is the enthalpy of vaporization of this liquid? Number J mol AH Vap Previous 3 Give Up & View Solution Check Answer Next Exit Hint

Explanation / Answer

x is 1/T

and,

y = lnP

Thus,

                       x                 y

Point 1      0.003077      1.209

Point 2      0.001600      2.139

Now,

rise = (y2-y1) = (2.139 - 1.209) = 0.930

run = (x2-x1) = (0.001600 - 0.003077) = -0.001477

Thus,

slope = rise/run = 0.930/(-0.001477) = -629.655

From the equation,

lnP = -dHv/RT

we have,

slope = -dHv/R

So,

dHv = -slope x R = -(-629.655) x 8.314 = 5234.952 J/mol

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