High School
SAT
ACT
University
MCAT
LSAT
DAT
Wize University Chemistry Textbook > Intermolecular Forces and Physical Properties

Vapor Pressure Cntd. (Clausius-Clapeyron Equation)

Properties of LiquidsPrevious Section
Phases of MatterNext Section
Popular Courses
Find My Course

Vapor Pressure Equation

Earlier we learned about vapor pressure. I've included an equation below that is sometimes tested on.

Vapor pressure: pressure exerted by the gaseous phase of a liquid that evaporated from the exposed surface of a liquid

Photo by HellTChi / CC BY

We can relate the vapor pressure of a substance at two different temperatures using the following equation.


** This equation only applies to vaporization or sublimation, it is a less general form of the Van't Hoff Equation.
checklist
Mark Yourself Question
  1. Grab a piece of paper and try this problem yourself.
  2. When you're done, check the "I have answered this question" box below.
  3. View the solution and report whether you got it right or wrong.

Practice: Heat of Vaporization for Hexane

Hexane is heated from 0oC to 50oC and the equilibrium vapor pressure increases from 0.06 atm to 0.53 atm.

a) Calculate the ΔvapH for hexanes.
b) The human nose can detect hexane at a partial pressure of 0.005 atm. Estimate the temperature at which we can no longer smell hexane.



Extra Practice
An alkane’s vapour pressure at 25.00 °C is 6.00 kPa. What is its vapour pressure at 80.00 °C if the enthalpy of vaporization is 43.0 kJ/mol? (Give your answer in kPa, do NOT include units in your answer)
Hexane is heated from 0oC to 50oC and the equilibrium vapour pressure increases from 0.06 atm to 0.53 atm.
1. Calculate the ΔHovap for hexanes. Report your answer in kJ/mol to three significant figures. Do not include units in your answer.
2. The human nose can detect hexane at a partial pressure of 0.005 atm. Estimate the temperature at which we can no longer smell hexane. Report your answer in K to three significant figures. Do not include units in your answer
Gas Pressure
What is the pressure (in mm Hg) of the gas inside the apparatus below if the outside pressure Patm = 750 mm Hg,
∆h1 = 40 mm and ∆h2 = 30 mm?
Vapour pressure
Assuming that the heat of vaporization is temperature independent what is the vapour pressure of water at 65oC? ΔvapHwater = 40.68kJ/mol .