2046chapter19

2046chapter19 - Chapter 19 Chemical Thermodynamics Entropy...

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1 Chapter 19 Chemical Thermodynamics Entropy and free energy Learning goals and key skills: h Understand the meaning of spontaneous process, reversible process, irreversible process, and isothermal process. h State the second law of thermodynamics. h Describe the kinds of molecular motion that a molecule can possess. h Explain how the entropy of a system is related to the number of accessible microstates. h Predict the sign of Δ S for physical and chemical processes. h State the third law of thermodynamics. h Calculate standard entropy changes for a system from standard molar entropies. h Calculate entropy changes in the surroundings for isothermal processes. h Calculate the Gibbs free energy from the enthalpy change and entropy change at a given temperature. h Use free energy changes to predict whether reactions are spontaneous. h Calculate standard free energy changes using standard free energies of formation. h Predict the effect of temperature on spontaneity given Δ H and Δ S. h Calculate Δ G under nonstandard conditions. h Relate Δ G ° and equilibrium constant. Energetics of solutions An endothermic process is not favored based on the change in enthalpy, yet they occur. Why? Recall that we must also look at the disorder ( entropy, S ) of the system. 0 th Law of Thermodynamics If A is in thermal equilibrium with B, and B is in thermal equilibrium with C, then C is also in thermal equilibrium with A. 1 st Law of Thermodynamics Energy of the universe is constant (conserved). Δ U = q + w q = heat absorbed by the system, w = work done on the system 2 nd Law of Thermodynamics In a spontaneous process, the entropy of the universe increases. ±S universe = ±S sys + ±S surr > 0 (if spontaneous) 3 rd Law of Thermodynamics The entropy of a pure crystalline substance at absolute zero is zero: S(0 K) = 0.
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2 Review Chapter 5: energy, enthalpy, 1 st law of thermo Thermodynamics : the science of heat and work Thermochemistry : the relationship between chemical reactions and energy changes Energy (E) The capacity to do work or to transfer heat. Work (w) The energy expended to move an object against an opposing force. w = F × d Heat (q) Derived from the movements of atoms and molecules (including vibrations and rotations). -q, heat evolved by the system (exothermic) +q, heat absorbed by system (endothermic) System System u E = q + w +w, work done onto the system -w, work done by the system Surroundings 1 st law of thermodynamics: the law of conservation of energy Energy is neither created nor destroyed Internal Energy = heat + work Δ E = q + w
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3 Enthalpy, H • the heat content of a substance at constant pressure. a
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This note was uploaded on 12/13/2011 for the course CHM 2046h taught by Professor Lufaso during the Fall '11 term at UNF.

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2046chapter19 - Chapter 19 Chemical Thermodynamics Entropy...

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