entropy and gibbs free energy

entropy and gibbs free energy - Week 6 Spontaneous...

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Week 6 Spontaneous Processes and Thermodynamic Equilibrium Nature of Spontaneous Processes Spontaneous forces exhibit a directionality (i.e. the arrow in the chemical reaction points in a certain direction, causing certain products to form certain reactants) o Heat flowing from a hot body to a cold one, never is it spontaneous in the other direction (there is no such thing as cold flowing) o A gas expanding into a region of lower pressure, never a gas spontaneously compressing itself o Diffusion of a particle until the concentration of the particle in the solvent is uniform, never the reappearance of the group of particles o Solute dissolving until uniformly distributed in the solvent, never spontaneously reforming its original crystalline structure. o At room temperature, ethanol will evaporate from a glass, but you will never (at room temperature) see it reappear in your glass. What is a spontaneous process? o One that, given a certain thermodynamic condition, happens “by itself”, and at those set conditions, is irreversible. o There are several factors that contribute to spontaneity that we will discuss in the following sections o Adiabatic expansion is an example of a spontaneous process. Entropy and Spontaneity: A molecular statistical interpretation Entropy o The numerical value of the entropy of a macroscopic system held in a particular thermodynamic state is a measure of the range of possible motions available to the molecules while the system is held in that particular thermodynamic state. o S = k B lnΩ Ω is the number of variable states k B = R/N 0 = gas constant/ avagadro’s number dimensions: J K -1 Entropy and Heat: Experimental Basis of the Second Law of Thermodynamics Carnot o Unrecoverable losses of energy to the environment cannot be completely eliminated, no matter how carefully the engine is designed o Thermodynamic efficiency, therefore, cannot be 100%
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This note was uploaded on 10/26/2011 for the course CHEM 20B taught by Professor Felker during the Spring '08 term at UCLA.

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entropy and gibbs free energy - Week 6 Spontaneous...

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