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Summary of week 4

This week you still examined the second law of thermodynamics, focusing on the actual entropy calculations.

The third law of thermodynamics is essential for estimation of entropy. The third law is the temperature principle. The third law leads to a conclusion that absolute zero temperature is never attainable. Based on the properties of entropy and the third law, entropy change was calculated for the reversible and irreversible processes.

The total entropy change of the reversible process such as a phase transition between solid and liquid at the melting point was zero demonstrating the second law principle.

The total entropy change of the freezing of supercooled liquid at -10 ℃ was positive suggesting that it is a spontaneous process according to the second law, consistent with our expectation.

Next week, you will examine the free energy functions. With free energies, You can determine the reversibility only with the system properties. Two important free energies, the Helmholtz free energy and the Gibbs free energy will be discussed. Then you will look at the physical meaning of free energies to see why they are called the ‘free energy’.

You will look at the thermodynamic potential energy as a capacity to do work. The thermodynamic potentials are also called as the fundamental functions. The four fundamental functions are internal energy U, enthalpy H, Helmholtz free energy F, and Gibbs free energy G. The differential form of thermodynamic potentials are called fundamental equations.

From fundamental equations, the famous property relations will be derived.

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This article is from the free online course:

Thermodynamics in Energy Engineering

Hanyang University

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