The Second Law of Thermodynamics

In physics and chemistry, we all study the concepts of thermodynamics. Thermodynamics deal with the concepts of heat and the various ways it gets transferred to one state from another state. Thermodynamics also talks about the losses that occur in the transfer of heat energy. There have been many laws proposed on the concepts of thermodynamics.

Thermodynamics and Various Laws

The branch of physics deals with heat energy and the work done in the system due to the conversion and the transfer of heat energy. Thermodynamics helps us to observe the larger change in the experiments that could be verified easily through the experimental studies carried out.

Concept of the system and surrounding in Thermodynamics

Systems and surroundings are synonymous with thermodynamics. While coming across these words in thermodynamics, it is important to know their importance. 

The system refers to anything we observe while everything apart from the system is called a surrounding. The system could be a large vessel, molecule, or any tiny entity. The universe in thermodynamics refers to the system plus surroundings.

There are three types of systems present in a thermodynamic experiment. They are namely:

1. An open system: An open system is a system that is in direct contact with the surrounding. In this type of system, as it has no boundary attached, the continuous exchange of matter and energy occurs between the system and the surroundings.
2. A closed system: A closed system is a system in which there is a boundary between the system and its surroundings. As there is a defined boundary, no interaction occurs between the system and the surroundings. So, no mass exchange, but only energy takes place between the system and the surroundings.
3. An isolated system: An isolated system is a system that doesn’t allow the exchange of either mass or energy between the system and the surroundings.

As a result, no exchange of mass and energy takes place. This system is hard to achieve because a perfect isolated system doesn’t exist in the real world.

Laws of Thermodynamics:

The various laws of thermodynamics are:

1. The first law of thermodynamics: The first law of thermodynamics states that energy cannot be created nor be destroyed. So, the form of energies can be changed.
2. The second law of thermodynamics: The second law of thermodynamics states that while one form of energy is converted to another, there is some loss during the conversion. 100% conversion of energy is not possible, and some loss occurs. So, the work done is not 100%.
3. The third law of thermodynamics: The third law of thermodynamics states that as the temperature reaches a value of absolute zero, the entropy of the system tends to become constant.

Second Law of Thermodynamics

As we know that energy can be converted from one form to another, the efficiency obtained is not 100 %. So, there’s a loss observed during the conversion.

Clausius, kelvin and Carnot came forward to propose another law of thermodynamics known as the ‘Second law of Thermodynamics.

The second law of thermodynamics elaborated on the first law of thermodynamics: energy can be changed from one form to another. The second law of thermodynamics also introduced another term known as Entropy.

Entropy Meaning

The degree of randomness or disorder in thermodynamics is termed Entropy.

So this means that when any energy is converted from one form to the other, the molecules are in random motion. So, it leads to an increase in the universe’s entropy overall. This increase in the entropy in the universe occurs from lower entropy to higher entropy to ensure that the system’s entropy increases in total.

Entropy is a state variable denoted by ‘S’ in thermodynamics. Heat is denoted by ‘Q’, and temperature is denoted by ‘T’ in thermodynamics. So, to calculate the change in the entropy of any system, we use the term ‘Delta S.’

So ‘ΔS’ equals the heat transferred (ΔQ) divided by temperature (T).

ΔS= ΔQ /T

There are two types of processes possible in nature. They are:

• Reversible Process

• Irreversible process

Entropy can be calculated for both reversible as well as irreversible processes.

Reversible process: A reversible process is a process when the gas can go back to its original state from the final state, and the entropy change that occurs in the process comes to be zero. When a liquid is forced to flow from a constricted pipe, it is an example of a reversible process.

A reversible process is sometimes referred to as an isentropic process because there is no entropy change observed.

Irreversible process: An irreversible process in which the gas doesn’t reach its initial state from its final state. The entropy change observed is not zero. It is observed that the entropy of the system and the surroundings increases in an irreversible process.

Conclusion

The second law of thermodynamics is the extension of the first law of thermodynamics that talks about the degree of randomness that occurs when the energy is converted from one form to another.

The leaking of air from the balloon and the melting of an ice cube are some real-life examples of the second law of thermodynamics.