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Entropy change can be determined by considering the difference in the initial and final state of a system. Entropy is an extensive property as it does not depend on heat conversion or path of heat exchange. Entropy refers to the degree of disorder or randomness of a system. Rudolf Clausius came up with the concept of entropy. Change in this degree of disorder in the system is entropy change. This change in entropy can be reversible or irreversible.
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Key Terms: Entropy, Entropy Change, Thermodynamics, System, Disorder, Randomness
Introduction to Entropy
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The degree of disorder or randomness of a system is known as Entropy. It is the thermal energy of a system that is not available for useful work. The concept of entropy was introduced in 1850 by German physicist Rudolf Clausius. Entropy functions while following the fundamental law of conservation of energy.
In thermodynamics, the behavior of the system is described using entropy. Behavior includes heat, temperature, pressure, and other thermodynamic properties.
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Introduction to Entropy Change
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Entropy change relies on the initial and final state of the system, regardless of the path taken. Entropy change can be reversible or irreversible. However, this nature of entropy does not affect the entropy change. The more disordered a system is the higher is the entropy.
Entropy increases when the molecules are more disordered than the reactants. The rearrangement or the change in the pattern of ions or atoms can also influence entropy during a chemical reaction.
When there is an addition of heat to the system, there is an increase in the movement of molecules. This leads to an increase in the disorder of the system. The disorder of particles in the system can also be measured with the help of temperature.
The change in entropy is inversely proportional to the temperature of the system. More the temperature of the system, the higher is the disorder.
Entropy Change
Entropy Change Formula
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The change in entropy can be determined by considering the difference in the initial and final state of a system.
So, \(\Delta\)S= Sf- Si
Where,
\(\Delta\)S denotes Entropy change.
Sf denotes final state.
Si denotes initial state.
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Entropy Change Expression
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The general expression for the change in entropy is:
\(\Delta\)S= qrevT
In the above equation, q is heat and T is temperature.
The ideal situation for the process is \(\Delta\)Stotal= \(\Delta\)Ssys+ \(\Delta\)Ssurr >0
This means that the change in entropy should be greater than zero.
Entropy Change Expression
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Entropy Characteristics
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The characteristics of entropy are:
- Mass of thermodynamical system influences entropy.
- Entropy can be denoted as the tendency of the universe to move towards randomness.
- Entropy is an extensive property as it does not depend on heat conversion or path of heat exchange.
- There is a constant increase in entropy of the universe.
- During the adiabatic process, the entropy change is zero. This is why the process has constant entropy.
Things to Remember
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- The degree of disorder or randomness of a system is known as Entropy. It is the thermal energy of a system that is not available for useful work.
- Entropy change can be reversible or irreversible.
- The change in entropy is inversely proportional to the temperature of the system.
- Entropy change formula: \(\Delta\)S= Sf- Si
- The general expression for the change in entropy is: \(\Delta\)S= qrevT
- The ideal situation for the process of entropy change is \(\Delta\)Stotal= \(\Delta\)Ssys+ \(\Delta\)Ssurr >0
- The more disordered a system is the higher is the entropy.
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Sample Questions
Ques. What is spontaneity? What is the relation between spontaneity and entropy? (3 Marks)
Ans. Spontaneity is a nature of a process. A process that is irreversible bust can be reversed using some external agents is called a spontaneous process. Once such a process starts, it doesn’t need external input of energy. The spontaneity of a process is largely defined and determined by the total change in entropy.
According to the second law of thermodynamics, there must be an increase in entropy for a reaction to being spontaneous.
Ques. What is a System? What are the different systems of Thermodynamics? (3 Marks)
Ans. The part of matter within a definite boundary on which the attention is focused is called the Thermodynamic system. The three types of systems are:
- Isolated System: The system that cannot exchange mass or energy with its surroundings is called an isolated system.
- Open System: The system in which the mass and energy can be exchanged and transferred in an open system.
- Closed System: The system in which the exchange of energy takes place but the exchange of mass does not take place in a closed system.
Ques. What is Entropy? What is Entropy Change? (3 Marks)
Ans. Entropy refers to the degree of disorder or randomness of a system. Entropy follows the fundamental law of conservation of energy. Entropy Change is the change in the degree of disorder in the system is entropy change. The change in entropy can be determined by calculating the difference between the initial and final state of a system. Entropy change can be reversible or irreversible. The change in entropy is inversely proportional to the temperature of the system.
Ques. What are the branches of Thermodynamics? (4 Marks)
Ans. There are four branches of thermodynamics:
- Classical Thermodynamics: In this branch, pressure and temperature are used to calculate other properties. The behavior of matter is examined using a macroscopic approach.
- Statistical Thermodynamics: The behavior of molecules is characterized by examining their properties and interaction with other molecules.
- Chemical Thermodynamics: In chemical thermodynamics, the relation of work and heat is studied during chemical reactions.
- Equilibrium Thermodynamics: The study of the transformation of any matter as it approaches the state of equilibrium comes under equilibrium thermodynamics.
Ques. Write a note on the thermodynamics process. (4 Marks)
Ans. When there is a change in the energy within the system, the system undergoes a thermodynamic process. Each thermodynamic process has a unique property. The four types of thermodynamic process are:
- Isothermal Process: The temperature remains constant throughout the isothermal process.
- Adiabatic Process: In the adiabatic process, no transfer of heat occurs in the system.
- Isobaric Process: The pressure remains constant throughout the isobaric process.
- Isochoric Process: In the isochoric process, the volume remains constant.
Ques. Explain the first law of Thermodynamics. (3 Marks)
Ans.The First Law of Thermodynamics is also known as the law of conservation of energy. It states that energy can neither be created nor be destroyed; it can only be transferred from one form to another. When a system is provided heat, some of the heat is used in doing work and some are used in changing the internal energy of the system. This law was stated by Rudolf Clausius and William Thomson.
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