### 1) The thermal property which remains constant during an adiabatic process is called as entropy.

i.e. dQ/T= constant

2) It is a measure of randomness or disorderliness of molecules.

3) It is independent of the path of thermal cycle.

4) The increase in entropy implies transition from ordered state to disorder state.

5) It is an index of unavailable energy of a system.

6) Entropy could also be termed as thermal inertia since more entropy results in less amount of heat energy being converted into work.

7) The increase in Entropy of a system implies transition of thermal energy from more available energy to less available form for conversion into work.

8) The net change in entropy is zero for any reversible cycle. This statement is called as clausius theorem.

9) Clausius Theorem: - The sum of quantities of heat transfer during the isothermal change divided by absolute temperature of the isothermal in a reversible cycle is zero. Entropy changes linearly in isothermal expansion and remains constant in adiabatic expansion or compression but decreases in isothermal compression.

**The shape of Temperature (T) - Entropy (S) diagram (Tephigram) is rectangle.**

10) Entropy increases in irreversible process.

11) Definition of second law of thermodynamics in terms of entropy

”Every chemical or physical or natural process in nature takes place in such a manner that total entropy increases or remains constant".

12) The principle of "degradation of energy" states that the available energy tending towards zero.

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