Vapor Pressure

Vapor Pressure - Chapter 4 Vapor Pressure p = Pressure of a...

Info iconThis preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 4 Vapor Pressure pº = Pressure of a substance in equilibrium with its pure condensed (liquid or solid) phase Why do we care? -spills -pesticide application -will lead us to Henry’s law constant
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Air Water Octanol A gas is a gas is a gas T, P Fresh, salt, ground, pore T, salinity, cosolvents NOM, biological lipids, other solvents T, chemical composition Pure Phase (l) or (s) Ideal behavior P o L C sat w C sat o K H = P o L /C sat w K oa K H K ow = C sat o /C sat w K ow K oa = C sat o /P o L
Background image of page 2
Ranges of p º (atm) PCBs – 10 -5 to 10 -9 n-alkanes – 10 0.2 to 10 -16 • n-C 10 H 22 ~ 10 -2.5 • n-C 20 H 42 ~ 10 -9 Benzene ~ 10 -0.9 toluene ~10 -1.42 Ethylbenzene ~ 10 -1.90 propyl benzene ~ 10 -2.35 carbon tetrachloride ~ 10 -0.85 methane 10 2.44 Even though VP is “low”, gas phase may still be important.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Phase diagram picture of three-phase diagram
Background image of page 4
Ideal Gas Law nRT pV = p = pressure V = volume n = moles of gas R = gas constant T = temperature (Kelvin)
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Thermodynamic considerations (deriving the van’t Hoff equation) 2 1 μ d d = consider a gas: if T or P is changed and equilibrium is re-established: the change in chemical potential in the two systems is equal dp V dT S d dp V dT S d 2 2 2 1 1 1 + - = + - = where S = molar entropy and V = molar volume 12 12 2 1 2 1 ) ( ) ( V S V V S S dT dp = - - =
Background image of page 6
at equilibrium S T H G G - = = - = 0 2 1 12 μ substituting: 12 12 V T H dT dp = for a liquid vaporizing, the volume change can be assumed to be equal to the volume of gas produced, since the volume of the solid or liquid is negligible 0 12 p RT V V gas = = Q. where did the n go? A. this is molar volume
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 12 0 0 ) ( RT H p dT dp = 2 12 0 ln RT H dT p d = dx du u dx u d 1 ln = recall (calculus!) where H 12 = H vap (gas) or H sub (solid) = energy required to convert one mole of liquid (or solid) to gas without an increase in T. H vap is a function of T. As T approaches the boiling point, H vap increases rapidly At T < boiling point, H vap increases slowly from 0-40ºC, H vap can be assumed to be constant The van’t Hoff equation
Background image of page 8
2 12 0 ln RT H dT p d = integrate assuming H vap is constant: a RT H p + = 12 0 ln B T A p + - = 0 ln Antoine equation if H vap is not constant: a c T b p + + - = 0 ln another Antoine equation
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 10
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 32

Vapor Pressure - Chapter 4 Vapor Pressure p = Pressure of a...

This preview shows document pages 1 - 10. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online