W17-Chem-260-L30_chemical_equilibrium_1 (1).pdf - 3/18/17...

This preview shows page 1 - 5 out of 10 pages.

3/18/171Chemistry 260Chemical PrinciplesLecture 30Wed Mar 22 2017Today in Chemistry 260üThe thermodynamics underlying chemical equilibrium.üChemical equilibrium in gas phase reac=ons.üChemical equilibrium for reac=ons in liquid solu=on.üChemical equilibrium for heterogeneous reac=ons.Next time in Chemistry 260Assigned reading: 6.4
3/18/172Chemical equilibrium (closed system):The number of moles of each component remains constant.Goal:To find the equilibrium composi=on of the system.Assump=on:Mechanical and thermal equilibrium, with uniformpressure and temperature throughout the system.,surrsurssrsysyTPPPTT====rate of establishingmechanical and thermRealaction requilibatesrium=The composi=on changes on a rela=vely slow =me scale,such that mechanical and thermal equilibria are maintained asthe chemical reac=on proceeds.Ques=ons regarding chemical reac=ons that thermodynamicsCANanswer:•What is the composi=on of a system at chemical equilibrium?• How does the equilibrium composi=on depend on otherparameters, such as temperature and pressure?•How fast will the chemical reac=on be, and how will the reac=onrate depend on external parameters such as pressure andtemperature? (this is the domain of kine=cs, molecular dynamics andnon-equilibrium sta=s=cal mechanics).WhatBASIC PRINCIPLEdictates the composi=on at chemicalequilibrium?The second law of thermodynamics! At constant temperature andpressure, the equilibrium composi=on of the reac=on mixture isthe one that minimizes the Gibbs free energy.Ques=ons regarding chemical reac=ons that thermodynamicsCANNOTanswer:
3/18/173Consider the chemical reaction: ABThe Gibbs energy change due to converting dnAmoles of Ainto dnBmoles of B(at constant Pand T): dG=μAdnA+μBdnBConservation of matter dictates: dnB=dnA=dξdG=μBμA()dξ⇔ ∂Gξ()T,P=μBμAΔrGAt equilibrium: dG=0⇔ ∂Gξ()T,P=0⇔ ΔrG=μBeqμAeq=0The chemical equilibrium condi1onGas phase reac1ons (ideal gas limit)A(g)B(g)μA=μA°+RTlnPAP°;μB=μB°+RTlnPBP°μBeqμAeq=0μB°μA°ΔrG°+RTlnPBeqP°lnPAeqP°()=ΔrG°+RTlnPBeqPAeq=ΔrG°+RTlnKP=0KP=PBeqPAeq=expΔrG°RT(KP= equilibrium constant in terms of partial pressures)A direct rela=onship between the chemical equilibriumconstant and the standard reac=on Gibbs energy!
3/18/174ΔGmix=RTxAlnxA+xBlnxB=RT(1ξ)ln(1ξ)+ξlnξ( ),where xB=ξ;xA=1ξddξΔGmix=RTln(1

Upload your study docs or become a

Course Hero member to access this document

Upload your study docs or become a

Course Hero member to access this document

End of preview. Want to read all 10 pages?

Upload your study docs or become a

Course Hero member to access this document

Term
Winter
Professor
STAFF

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture