A) To a 1L flask that contains air at a pressure of 101 kPa a small amount of li
ID: 913730 • Letter: A
Question
A) To a 1L flask that contains air at a pressure of 101 kPa a small amount of liquid is added. The pressure in the flask after the addition of the liquid is 107 kPa. What is the vapor pressure of the liquid?
B)The slope in a plot of lnPvap vs. (1/T) for an unknown liquid is found to be -1,141. What is the value of Hvap for the liquid in units of kJ/mol?
C)A 5 mL sample of an unknown liquid is placed into a 250 mL flask that has had all of the air removed. The pressure measured in the flask is found to be 32.2kPa. In a seperate trial the student puts 214 mL of the same liquid into the same flask at the same conditions. What will the pressure measure (in kPa) in the second trial?
Explanation / Answer
A)Given,
Total pressure = 107 kPa
Pressure of air = 101 kPa
total pressure = pressure of the air + vapor pressure of the liquid
Vapor pressure of the liquid = Total pressure - Pressure of air
= 107 - 101 kPa
Vapor pressure of liquid = 6 kPa
B)
According to Clausius-Calyperon equation
lnP=- Hvap/R+ C
slope = -Hvap/R =-1141 where, R=8.314 J/K.mol
Hvap =1141*8.314
=9486.3 J/mol
Hvap =9.5 kJ/mol
C) 5 mL liquid exerts pressure = 32.2 kPa
1 mL liquid exerts pressure = 32.2/5 = 6.44 kPa
214 mL liquid exerts pressure = 214*6.44
= 1378.16 kPa
214 mL liquid exerts pressure = 1380 kPa
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