Grade:Upto college level

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AKASH GOYAL AskiitiansExpert-IITD
420 Points
12 years ago

Dear Student

The extent of disorder or randomness in a system may be expressed by a property known as entropy. Entropy may be termed as the property of a system which measures the degree of disorder or randomness in the system. It is generally expressed by the symbol, S. Entropy like internal energy and enthalpy, is a state function and change in entropy therefore, depends only on the initial and final states of the system. The change in entropy during the process when a system undergoes a change from one state to another is represented by DS. Thus, DS = S(final state) - S(initial state) and for chemical reactions, DS = S(products) - S(reactants). For a reversible process at equilibrium, the change in entropy may be expressed as:

DS = qrev / T

where qrev represents the heat supplied at temperature T in a reversible process.

Units of entropy

Since entropy change is expressed as heat divided by temperature, the units of entropy are calories per degree (expressed as entropy units eu) or joules per kelvin, JK-1 (expressed as EU).

Physical meaning of Entropy

The physical meaning of entropy is that entropy is a measure of degree of disorder (or randomness) of a system. The relation between entropy and disorder provides a suitable explanation for entropy change in various processes. The greater the disorder in a system, the higher is the entropy. Obviously, for a given substance the solid state is the state of lowest entropy (most ordered state), the gaseous state is the state of highest entropy and the liquid state, is intermediate between the two. In the case of mixing of two gases when the stopcock is opened, the gases mix to achieve more randomness or disorder. In this case, there is no exchange of matter or energy between the system and the surroundings. The change occurs from ordered state (less entropy) to disordered state (higher entropy). Thus the change in entropy is positive.


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