lecture_2legge - Classical Thermodynamics Thermodynamics...

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1 Thermodynamics and chemical equilibria Lecture 2 8/27/09 • Lecture 2 • Chapter 1 Voet, Voet and Pratt Classical Thermodynamics • Key goals for today’s lecture: – Define: • Gibbs Free Energy ( G ) G = H - TS • Thermodynamics as a prediction as to the spontaneous nature of a chemical reaction A + B C • State Functions • First and Second Laws • Heat, work, internal energy, enthalpy, entropy, free energy, chemical potential, System, property, state, adiabatic, diathermal, reversible • Equilibrium constants Gibb’s Free Energy • Is a state function (a property of a system that depends only on the current state of the system and not its history) • Gibb’s Free Energy is determined at constant T and P : G = H TS •T h e Gibbs free energy ( G ) of a system is defined by an enthalpy term ( H ) (change of the total energy with the system), and the entropy term ( S ) (change in the disorder) at temperature ( T ) G H - TS Δ G ° = H -T S Thermodynamic Definitions: (What is Enthalpy and Entropy and their relationship to the First and Second Laws?) First, Let’s Define a System a defined part of the universe a chemical reaction bti a bacteria a reaction vessel a metabolic pathway Surroundings : the rest of the universe Open system : allows exchange of energy and matter Isolated system : no exchange of matter or energy. i.e. A perfect insulated box . Reversible and Irreversible Processes • Reversible processes – Proceed infinitesimally out of balance. – Requires zero friction, epsilon heat gradients – Are hypothetical only F surr • Irreversible process – “Real world” process – Have finite changes and loses. F sys P sys F sys = F surr + dF First Law of Thermodynamics: Energy is Conserved Energy is neither created or destroyed. – In a chemical reaction, all the energy must be accounted for. Equivalence of work w and energy (heat) q – Work (w) is defined as w = F x D (organized motion) – Heat (q) is a reflection of random molecular motions (heat) Heat q : If q is positive reaction is endothermic system absorbs heat from surrounding – If is positive reaction is endothermic system absorbs heat from surroundings –I f q is negative exothermic system gives off heat. Work w: f w i s positive , the system does work ON the surroundings. Remember sign conventions of thermodynamics from a steam engine Δ E=q-w Δ E=(-q)-(+w) Control Volume: Defines the system boundary Piston displacement DOES work(+w) on surroundings Cylinder “Feels” hot as it looses heat (-q) to surroundings
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2 Direction of heat flow by definition is most important .
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lecture_2legge - Classical Thermodynamics Thermodynamics...

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