Chem 402 Lecture 30: L30 4:7:17

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University College - Chemistry
University College - Chemistry Chem 402
Barnes Alexander

7 April 2017 L30: Colligative Properties and Two-Component Phase Equilibria I. Vapor Pressure A. Vapor Pressure of Systems 1. Effect of an inert gas pressure on vapor pressure over a liquid or solid a. Total pressure p = p +ap inert β€’ p0is the equilibrium vapor pressure of pure A at temperature T β€’ pAis the equilibrium partial pressure of A in the presence of inert gas β€’ 𝑝𝐴is the vapor pressure of a pure liquid b. p Ancreases as you add inert gas due to entropy of mixing β€’ Lowers the  oA the gas, and thus more molecules move from the liquid to gas phase since the chemical potential of gas is lower β€’ Think S = π‘˜π‘™π‘›Ξ©: more microstates in gas phase because of mixing with inert gas c. From our microscopic understanding of entropy and total number of discrete microscopic configurations β€’ If there is inert gas above the liquid, there will be entropy of mixing if the vapor pressure of the liquid increases d. In terms of LeChatelier’s Principle β€’ Adding inert gas in increases p inert β€’ To decrease that stress of added p inertiven some total pressure, must increase pAby drawing molecules into gas phase from liquid to increase p and A decrease p inertlook at mole fractions as well) 2. Application of Inert Gas vapor pressure a. For ultra high vacuum in the cyclotron resonance masen (gyrotron) β€’ Gives microwave power at 200 GHz to improve NMR sensitivity for structure and dynamics - - b. In the apparatus, there is an e gun that directs an e beam through the system but this requires really low pressures β€’ Low pressures to prevent gas molecules from interacting with e beam or other unfavorable reactions -9 -12 β€’ Need pressures around 10 torr (= 10 atm) c. In the tubes, there is water adsorption, which creates some 𝑝 𝐻 𝑂 , which makes it -5 2 difficult to pump out gas below 10 torr d. Then, N g2s is backfilled in to get all the H O2into the gas phase, then all the gas is pumped out to immediately get to 10 torr β€’ Application of using inert gas to increase p to get water out of this system to A lower pressure to needed levels πœ•π‘π΄ B. Finding p Ap), the slope = ( ) πœ•π‘ 𝑇 1. At equilibrium we know that  𝑔,𝑇,𝑝 (𝑝) 𝐴  𝑙,𝑇,𝑝 ( 𝐴) πœ• πœ• 𝐴 πœ• 𝐴 2. Take of both sides: (𝐴(𝑔,𝑇,𝑝 𝑝𝐴)) = ( 𝐴,𝑇,𝑝 )𝐴 ) πœ•π‘ πœ•π‘ πœ•π‘ a. Note that the left side requires a chain rule becauseAp (p) is a function of p πœ•ο­π΄,𝑔 πœ•π‘π‘Ž πœ•ο­π΄(𝑙,𝑇,𝐴) 3. ( ) ( ) = ( ) πœ•π‘π΄ 𝑇 πœ•π‘ 𝑇 πœ•π‘ 𝑇 a. Looking at our fundamental equation: 𝑑 = 𝑑𝐺 = βˆ’π‘†π‘‘π‘‡ + 𝑉𝑑𝑝 Μ… πœ•ο­ b. We know that ( ) = 𝑉 Μ… πœ•π‘ 𝑇 Μ… πœ•π‘π‘Ž Μ… πœ•π‘ π‘Ž 𝑉̅𝑙 4. 𝑉 𝑔 (
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