BasicThermo2

BasicThermo2 - MSE 3050, Phase Diagrams and Kinetics,...

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Unformatted text preview: MSE 3050, Phase Diagrams and Kinetics, Leonid Zhigilei Review of classical thermodynamics Fundamental Laws, Properties and Processes (2) Entropy and the Second Law Concepts of equilibrium Reversible and irreversible processes The direction of spontaneous change Entropy and spontaneous/irreversible processes Calculation of entropy in isochoric and isobaric processes Calculation of entropy in reversible and irreversible processes Reading: Chapters 3.1 3.5, 3.14 3.17 of Gaskell or the same material in any other textbook on thermodynamics MSE 3050, Phase Diagrams and Kinetics, Leonid Zhigilei 2 nd Law of Thermodynamics A system left to itself will either 1. Remains in the same state indefinitely (system is in equilibrium ). The system will move from the equilibrium state only if acted on by some external impact. 2. Will move, of its own accord, to some other state. The system in this case is in a non-equilibrium state and will move towards equilibrium state in a natural or spontaneous process. Spontaneous transition from non-equilibrium state to the equilibrium state cannot be reversed without application of an external force it is an irreversible process. Examples of spontaneous/irreversible processes: Mixing of different gases Heat flow from hot to cold objects T 1 < T 2 T 1 = T 2 Spontaneous processes are not necessarily instantaneous processes kinetics! MSE 3050, Phase Diagrams and Kinetics, Leonid Zhigilei How to predict which process will proceed spontaneously? 1 st law: U and H are state functions - if the system is going from A to B, ' U(A o B) = - ' U(B o A) or ' H(A o B) = - ' H(B o A) But fist law does not tell us which reaction, forward or reverse is natural or spontaneous one. Intuition: The energetic driving force- the tendency to fall to a lower potential energy, e.g. release heat in a reaction. Indeed, often spontaneous changes are exothermic (reaction produces heat), e.g. H 2 (gas) + O 2 (gas) o H 2 O (liquid) ' H = -286 kJmol-1 But , reactions can also occur spontaneously which are endothermic, e.g. H 2 O (liquid,105 q C) o H 2 O (gas,105 q C) ' H = +44 kJmol-1 A negative sign of ' H favors but does not guarantee spontaneity. ' H A B MSE 3050, Phase Diagrams and Kinetics, Leonid Zhigilei Quantification of irreversibility It is desirable to find some common measure of the tendency of a system to change spontaneously. This measure should be A thermodynamic property (state function). It should change in a characteristic manner (e.g. always increase) when a process proceeds spontaneously....
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BasicThermo2 - MSE 3050, Phase Diagrams and Kinetics,...

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