What is Entropy?
The decrease in enthalpy may contribute to the spontaneity of a process but it cannot explain spontaneity in all the cases. Since we acknowledge many spontaneous endothermic reactions around us. For example, an isothermal reversible expansion of an ideal gas, where change in enthalpy,
ΞH= 0
Hence, we define a new state function to explain the spontaneity of a process. This state function is named entropy. Entropy is generally defined as the degree of randomness of a macroscopic system.
Internal interactions between various subsystems give multiple entropy changes.
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What is Entropy Change?
Since entropy is a state function, the entropy change of a system depends only on the initial and final state irrespective of the path taken. Hence, change in entropy does not differ with the nature of the processes either reversible or irreversible.
Thus, the greater the disorderliness in an isolated system, the higher is the entropy. In a chemical reaction, the change in entropy can also be attributed to the rearrangement of atoms or ions from one pattern to another. In the products, if the molecules are very much disordered in comparison to the reactants, there will be a resultant increase in entropy during the reaction. Thus, the change in entropy accompanying a chemical reaction can be estimated qualitatively by considering the disorderliness of the structures of the species involved in the reaction. For example, the crystalline solid state generally exhibits lower entropy in comparison to other solids.
The addition of heat to a system increases the randomness in the system due to an increase in molecular motions. Generally, a system at a higher temperature has greater randomness than at a lower temperature. Thus, temperature too helps in the measurement of the randomness of particles in a system. Heat added to a system at a lower temperature causes greater randomness than in comparison to when heat is added to it at a higher temperature. Thus, the entropy change is inversely proportional to the temperature of the system.
Expression for entropy change
The general expression for entropy change can be given by:
Where,
For a spontaneous process, entropy change for the system and the surrounding must be greater than zero, that is
The general expression can be given as:
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Entropy
Frequently Asked Questions β FAQs
What is Entropy?
Can entropy ever decrease?
Can entropy be infinite?
Can entropy be negative?
What causes entropy?
More energy put into a system excites the molecules and the amount of random activity.
As the gas expands in a system, entropy increases.
For more information on the entropy formula and the effect of entropy on the spontaneity of a process, download BYJU’S – The Learning App.
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