Calculation of entropy change

The entropy, Spontaneous vs non-spontaneous, Reversible and irreversible processes, Calculation of entropy changes (Isothermal, isobaric, isochoric, adiabatic), Phase changes at equilibrium, Trouton s rule, Calculation for irreversible processes... 

Calculation of Entropy Change, AS, for Reversible Expansion Process... 

Although derived for a reversible process, this equation relates properties only, and is independent of the process causing the change of state. It is therefore a general equation for the calculation of entropy changes of an ideal gas. 

The thermodynamic temperature is identical to the ideal-gas temperature. Both will be referred to as the absolute temperature. From here on we will use the absolute temperature for the calculation of entropy change according to dS = bqlT. 

What property of entropy allows Hess s law to be used in the calculation of entropy changes ... 

In equilibrium thermodynamics model A and in model B not far from equilibrium (and with no memory to temperature) the entropy may be calculated up to a constant. Namely, in both cases S = S(V, T) (2.6)2, (2.25) and we can use the equilibrium processes (2.28) in B or arbitrary processes in A for classical calculation of entropy change by integration of dS/dT or dS/dV expressible by Gibbs equations (2.18), (2.19), (2.38) through measurable heat capacity dU/dT or state Eqs.(2.6>, (2.33) (with equilibrium pressure P° in model B). This seems to accord with such a property as in (1.11), (1.40) in Sects. 1.3, 1.4. As we noted above, here the Gibbs equations used were proved to be valid not only in classical equilibrium thermodynamics (2.18), (2.19) but also in the nonequilibrium model B (2.38) and this expresses the local equilibrium hypothesis in model B (it will be proved also in nonuniform models in Chaps.3 (Sect. 3.6), 4, while in classical theories of irreversible processes [12, 16] it must be taken as a postulate). 

Figure 4-3 Path for the calculation of entropy changes in the ideal-gas state.

Equations 131-1 AO allow the calculation of entropy changes for a pure substance in any state of aggregation [3]. 

EXAMPLES. Calculation of Entropy Change for an Irreversible, Isothermal Compression A piston-cylinder device initially contains 0.50 of an ideal gas at 150 kPa and 20°C. The gas is subjected to a constant external pressure of 400 kPa and compressed in an isothermal process. Assume the surroundings are at 20 C. Take Cp = 25R and assume the ideal gas model holds. (a) Determine the heat transfer (in kj) during the process. (b) What is the entropy change of the system, surroundings, and universe (c) Is the process reversible, irreversible, or impossible ... 

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