A certain liquid has a vapor pressure of 92.0 Torr at 23.0 °C and 372.0 Torr at 45.0 °C. Calculate the value of ΔH°vap for this liquid.
Update:Calculate the value of the normal boiling point of this liquid. the Hvap for this liquid is 47900J.
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Answer
Part1
By Clausius-Clapeyron equation
logP2/P1 = delta H/(2.303*R) * (1/T1-1/T2)
P1=92 torr P2=372, T1=296k, T2=318
deltaH = heat of vaporisation in cal/mole
T2 and T1 are temp in kelvin
R=1.99 cal/mole-k
log372/92=0.6067
2.303*R=2.303*1.99=4.5829cal/mole-k
1/T1-1/T2=0.0002337K
Therefore, deltaH=0.6067*4.5829/0.0002337 =11897 cal or 11897/239kj=49.78kj
Part2
Let normal boiling point is T2
Corresponding vap pressure P2 would be atm pr =760 torr
log760/92=0.9170 , P1=92 torr
2.303*R=2.303*1.99=4.5829cal/mole-k
1/T1-1/T2= (1/296-1/T2) , T1=273+23=296k
1/T1-1/T2=( 0.003378 - 1/T2)
Heat of vaporisation = 47.9kj given=47.9*239cal = 11448cal 1 kJ = 239.0057
Therefore, 0.9170*4.5829/11448=0.003378-1/T2
0.0003671=0.003378-1/T2
1/T2=0.003378-0.0003871=0.0030109
T2=332K or 59 degc
I did it myself and it turns out the Answer above is actually the correct answer (both parts) however sapling chooses to be a dick in require that you enter 4 significant figures so therefore your answer will be 49.750