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Unformatted text preview: 1 Announcements Monday, Oct. 25, in class. Covers Lectures 115 Chapters 18 Midterm LECTURE 16 Bring: calculator equation sheet (make your own) Last Time Path Dependence of Heat and Work Irreversible Work and Heat Work and Free Energy Chemical Work and Chemical Potential Superconductivity and Magnetic Work 2 Today Chapter 9 (part 1) Gibbs Free Energy and Chemical Reactions LECTURE 16 Gibbs Free Energy, and why chemists like it. Law of Mass Action Examples: Chemical reactions, pH Kinetic of chemical reactions Catalysis Enthalpy and Gibbs Free Energy Enthalpy: H U + pV ≡ Important for processes at constant p It is energy of system + energy required to vacate the volume occupied by the system, i.e. this is total energy required to create a system in a space that is initially not vacant. Processes at constant pressure: 1. No effective work is done : & Q= dH Example: evaporation of liquid in open jar. Heat of vaporization = Δ H 2. Constant T and p : ( ) & Q= d = d τ σ τσ & W' = dF +d(pV)= dG & W = dF Isothermal: ( ) & W' = & W +d pV = dH  & Q Gibbs Free Energy: G F + pV =U + pV  τσ ≡ L e c t u r e 1 5 3 Gibbs Free Energy Chemists like the Gibbs Free Energy, because it is in variables they like and often call it just “free energy” What are the proper control variables of G? G F + pV =U + pV  τσ ≡ Gibbs Free Energy plunger pressure reservoir temperature reservoir system Notice that under these conditions of using τ , p, N as the control variables, the Gibbs free energy is minimized: G is an extremum because dG = 0 G is minimized, because entropy is maximized. G U  pV τσ ≡ + ( ) G = G N, , p U  pV τ τσ ≡ + dG =  d Vdp+ dN σ τ μ + 4 Gibbs Free Energy Fixed τ , p, N : Gibbs energy is minimized ( ) G N, , p U  pV τ τσ ≡ + Fixed τ , V, N : Helmholtz energy is minimized dG =  d Vdp+ dN σ τ μ + ( ) F N, ,V U  τ τσ ≡ dF d pdV dN σ τ μ =  + plunger pressure reservoir temperature reservoir system Differential relations: Set pressure p and N constant: Similar manipulations lead to: Gibbs Free Energy ( ) G = G N, , p U  pV τ τσ ≡ + dG =  d Vdp+ dN σ τ μ + 5 plunger pressure reservoir temperature reservoir system G is extensive, but it is a function of: extensive intensive intensive When G is expressed in terms of...
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This note was uploaded on 12/14/2010 for the course PHYSICS 416 taught by Professor Savikhin during the Spring '10 term at Purdue.
 Spring '10
 SAVIKHIN
 Physics, Energy, Work, Heat

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