Entropy and Irreversibility | MIT 5.60 Thermodynamics

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Entropy for Isolated Systems
Entropy of the Universe
Heat Flow and Entropy
Joule Expansion Entropy
Entropy of Mixing
Heating and Cooling Entropy
Phase Change Entropy

Entropy for Isolated Systems

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Playing Section
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    For any spontaneous process in an isolated system, delta S is always greater than or equal to zero.

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    This principle dictates the direction of natural change within the system.

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    Entropy change is zero only for perfectly reversible processes in isolation.

The First Law of Thermodynamics, including the concepts of heat (q), work (w), internal energy (U), and enthalpy (H).
The conceptual distinction between thermodynamic reversibility (quasi-static processes) and irreversibility.
The mathematical definition of state functions (path-independence) versus path functions.
The Carnot Cycle and its efficiency, which establishes the foundation for the thermodynamic temperature scale.
The Second Law of Thermodynamics and the concept of entropy generation in the universe (spontaneity criteria).
Defining Helmholtz and Gibbs Free Energy as thermodynamic potentials to predict spontaneity at constant temperature and pressure.
Statistical Thermodynamics and Boltzmann's microscopic interpretation of entropy based on microstates.
The Third Law of Thermodynamics and the determination of absolute entropies.
Applying entropy and free energy calculations to chemical equilibria and physical phase transitions.
95.7K views424likes52:44@mitocwOriginal Release: 2008-12-12

For an isolated system, entropy change (ΔS) is always greater than or equal to zero for any spontaneous process, with ΔS > 0 for irreversible processes and ΔS = 0 for reversible processes. This principle, derived from the Clausius inequality, determines the direction of spontaneous change. For non-isolated systems, the total entropy of the universe (system plus surroundings) never decreases. Entropy changes for common processes are calculated by constructing reversible paths: for heat transfer between bodies at different temperatures, ΔS = ∫dq/T; for ideal gas expansion, ΔS = nR ln(V2/V1); for mixing, ΔS = -nR(x_A ln x_A + x_B ln x_B); and for phase transitions, ΔS = ΔH/T at equilibrium.