Lect+12+08

Lect+12+08 - Lecture 12 A Distillation Problem...

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• nmgarof
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Lecture 12 A Distillation Problem Thermodynamics - Energy Distillation - a plain language understanding and a distillation example The First law of thermodynamics - The Energy of the universe remains constant or Energy is conserved The definition of Internal Energy “E” combines two path dependant function to create a state function the internal energy ; E = q+w which is especially useful at constant volume. A second state function Enthalpy “H” is especially useful at constant pressure H = E + (PV) The relationship between energy transfer into/out-of a system and the change of the system’s temperature is defined by the heat capacities.

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Toluene- Benzene distillation 11.61 At 293K • P ° tol = 0.02898 atm and P ° ben = 0.0987 Equal number of moles of moles of toluene and toluene and benzene are mixed and form an ideal solution. QUESTION? Determine the mole fraction of benzene in the vapor phase at equilibrium
P-X diagram Benzene has a higher vapor pressure- component 1 Toluene has a lower vapor pressure - component 2 What will happen in this case?

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Raoult’s law can be used for ideal solution vapor pressures so • P ben = X ben P ° ben • P tol = X tol P ° tol Equal number of moles so X tol =X ben = 0.5 (for liquid) • P ben = 0.500(0.0987 atm) = 0.0493 atm • P tol = 0.500(0.0289 atm) = 0.0144 atm and PV = nRT so for ideal gas • n ben = P ben (V/RT) and similarly for toluene • X ben = X ben /( X ben +X tol ) = P ben /(P ben + P tol ) = 0.77 Solution benzene mole fraction is 0.50. Vapor benzene mole fraction is 0.77.
“The Energy of the Universe is Constant The First Law of Thermodynamics E = q + w Different Forms of energy: kinetic energy, potential energy, internal energy, thermal energy, chemical energy Heat (q) - transfer of thermal energy- Microscopic energy heat capacity, specific heats heat balance problems Work (w) - transfer of energy in an organized form - Macroscopic energy calculating expansion work

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The First Law of Thermodynamics System Boundary Surroundings E + E = E Energy can cross the boundary as heat or work The Universe is the System plus Surroundings
Systems, States and Processes System - the part of the universe we are interested in Surroundings - the part of the universe that can exchange matter and energy with the system Closed system - no matter exchange with the surrounding Open system - matter exchange with surroundings Adiabatic system - no energy transfer across the boundary Isothermal system - constant temperature at the boundary

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What is Equilibrium?
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• Spring '08
• SHARP

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