CHM102_Chapter 18 class notes

CHM102_Chapter 18 class notes - 12/29/2010 Chapter 18...

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12/29/2010 1 Chapter 18 Thermodynamics and Equilibrium Contents and Concepts 1. First Law of Thermodynamics 2. Entropy and the Second Law of Thermodynamics 3. Standard Entropies and the Third Law of Thermodynamics Spontaneous Processes and Entropy A spontaneous process is one that occurs by itself. As we will see, the entropy of the system increases in a spontaneous process.
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12/29/2010 2 Free-Energy Concept The quantity Δ H – T Δ S can function as a criterion for the spontaneity of a reaction at constant temperature, T, and pressure, P. By defining a quantity called the free energy, G = H – TS, we find that Δ G equals the quantity Δ H – T Δ S, so the free energy gives us a thermodynamic criterion of spontaneity. 4. Free Energy and Spontaneity 5. Interpretation of Free Energy Free Energy and Equilibrium Constants The total free energy of the substances in a reaction mixture decreases as the reaction proceeds. As we discuss, the standard free-energy change for a reaction is related to its equilibrium constant. 6. Relating Δ G ° to the Equilibrium Constant 7. Change of Free Energy with Temperature
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12/29/2010 3 Thermodynamics is the study of heat and other forms of energy involved in chemical or physical processes. First Law of Thermodynamics • The first law of thermodynamics is essentially the law of conservation of energy applied to a thermodynamic system. • Recall that the internal energy, U , is the sum of the kinetic and potential energies of the particles making up the system: Δ U = U f U i
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4 • Exchanges of energy between the system and its surroundings are of two types : heat, q , and work, w . • Putting this in an equation gives us the first law of thermodynamics. Δ U = q + w Sign Convention for q and w • When heat is evolved by the system, q is negative . This decreases the internal energy of the system. • When heat is absorbed by the system, q is positive . This increases the internal energy of the system. Here the system expands and evolves heat from A to B. Zn
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CHM102_Chapter 18 class notes - 12/29/2010 Chapter 18...

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