Courses
Courses for Kids
Free study material
Offline Centres
More

# The Second Law of Thermodynamics

Last updated date: 30th Nov 2023
Total views: 21.3k
Views today: 0.21k

## Second Law of Thermodynamics

When a hot object comes into contact with a cold object, heat flows from the hotter to the colder, never from colder to hotter spontaneously. Energy may still be conserved if heat left the cooler object and went to the hotter one. That’s where one encounters the second law of thermodynamics.

The second law of thermodynamics states that the entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible in nature. The systems are isolated and spontaneously evolve towards thermodynamic equilibrium, the state with maximum entropy.

The entropy which is of the total surroundings and the system can remain constant in ideal cases that are where the system is in thermodynamic equilibrium, or we can say is undergoing a (fictitious) reversible process in nature. In all processes that are occurring, including spontaneous processes, the total entropy of the system and its surroundings increases and the process is irreversible in nature and also in the thermodynamic sense. The entropy increase accounts for the irreversibility of natural processes, and the asymmetry which is between past and future.

Historically, if we look at the second law, it was an empirical finding that was accepted as an axiom of thermodynamic theory. classical mechanics, statistical mechanics, or quantum mechanics, explains the microscopic origin of the law.

The second law of thermodynamics has been expressed in numerous ways. This law’s first formulation is credited to the French scientist named Sadi Carnot, who in 1824 showed that there is an upper limit to the efficiency of conversion of heat to work in a heat engine. This aspect of the second law of thermodynamics is often named after Carnot.

### Various Statements

The second law of thermodynamics can be expressed in numeric specific ways, the most prominent classical statements being the statement by Rudolf Clausius (1854), the statement by Lord Kelvin in1851, and by the statement in axiomatic thermodynamics by Constantin Caratheodory in 1909. These statements of different scientists cast the law in general physical terms citing the impossibility of certain processes. The scientists,  Clausius, and Kelvin's statements have been shown to be of equal importance.

### Equation for Second Law of Thermodynamics

Stoichiometrically, the second law of thermodynamics is represented as:

ΔS(univ) > 0

where ΔS(univ) is the change in the entropy of the universe.

Entropy is a measure of a system's randomness, as well as a measure of energy or chaos within a closed system. It may be thought of as a quantitative metric for describing energy quality.

Meanwhile, there are just a few causes that cause the closed system's entropy to rise. To begin with, in a closed system, heat is exchanged with the environment while the mass remains constant. This change in heat content causes a disruption in the system, increasing the entropy of the system.

Second, intrinsic modifications in the system's molecular motions are possible. This produces disruptions, which in turn cause irreversibilities inside the system, increasing the entropy of the system.

### Carnot's Principle

As per history, the origin of the second law of thermodynamics was in scientists Carnot's principle only. The law refers to a cycle of a Carnot heat engine, fictively operated in the limiting mode of extreme slowness known as quasi-static so that the work and heat transfers are only between subsystems that are always in their own internal states of thermodynamic equilibrium. The engine of Carnot is an idealized device that is of special interest to engineers who are concerned with the efficiency of heat engines. The principle of Carnot was recognized by Carnot at a time when the caloric theory of heat was seriously taken into consideration, before the recognition of the first law of thermodynamics, and before the expression of mathematics of the entropy concept.  Interpreted iIn the light of the law, it is physically equivalent to the second law of thermodynamics and remains valid today. Carnot's original arguments were considered from the viewpoint of the caloric theory and before the discovery of the first law of thermodynamics. Some samples from his book are given below:

The German scientist Rudolf Clausius in 1850 had also laid the foundation stone for the second law of thermodynamics by examining the relationship between heat transfer and work. His formulation of the second law of thermodynamics, which was published in Germany in 1854, is known as the Clausius statement:

Heat can never pass from a colder to a warmer body without having some of the other changes which are connected, occurring at the same time.

### Planks Proposition

Planck offered the following proposition which was derived directly from his own experience. This is sometimes regarded as his statement of the second law of thermodynamics, but he postulated it as a starting point for the derivation of the second law.

It is impossible to construct an engine that will work in a complete cycle, and produce no effect except the cooling of a heat reservoir and raising of a weight.

The relationship was between Kelvin's statement and Planck's proposition.

It is almost customary in textbooks nowadays, to speak of the "Kelvin–-Planck statement" of the second law, as if we take an example in the text by Ter Haar and Wergeland.

The Kelvin–Planck statement or we also call it the heat engine statement of the second law of thermodynamics states that:

It is impossible to devise a device that is cyclically operating and the sole effect is- to absorb energy in the form of heat from a single thermal reservoir and to deliver an equivalent work to all.

### Planck's Statement

The statement in which Planck stated the second law is as follows:

Every process which is occurring in nature proceeds in the sense in which the sum of the entropies of all bodies taking part in that process is increased. In the limit, for example for reversible processes, the sum of the entropies remains unchanged.

### Planck's Principle

Max Planck in 1926 wrote a very important paper on the basics of thermodynamics. He indicated the principle as follows:

The internal energy of a closed system is increased by an adiabatic process, throughout the duration of which, the volume of the system remains constant.

This formulation does not mention temperature and does not mention heat, nor even entropy, and does not necessarily implicitly rely on those concepts, but it implies the content of the second law in thermodynamics. A statement that is closely related is that "Frictional pressure never does positive work." Planck also wrote: "The production of heat by the friction is irreversible."

If we are not mentioning entropy, this principle of Planck is stated in physical terms. It is very closely related to the Kelvin statement which was explained above. It is relevant that for a system at a mole number and constant volume, entropy is a monotonic function of the internal energy.

### Clausius's Statement

It is impossible to construct a device operating in a cycle that can transfer heat from a colder body to a warmer one without consuming any work. Also, energy will not flow spontaneously from a low-temperature object to a higher-temperature object. It's vital to understand that we're talking about energy transfer on a net basis. Transfer of energetic particles or electromagnetic radiation can transfer energy from a cold object to a hot object. In any spontaneous process, however, the net transfer will occur from the hot object to the cold object. In order to move the net energy to the heated item, some type of labour is required. In other words, the refrigerator will not work unless the compressor is powered by an external source. Clausius's statement is used by the heat pump and refrigerator.

### Conclusion

The thermodynamics second law states that the entropy of an isolated system can never decrease over time and is constant if and only if all processes are reversible in nature. Entropy is a measure of a system's randomness, as well as energy or chaos within a closed system.

## FAQs on The Second Law of Thermodynamics

1. State the second law of thermodynamics.

The second law of thermodynamics states that the entire universe entropy as an isolated system will always increase over time. The change in the entropy in the universe can never be a negative state, the second law of thermodynamics. The direction of heat transmission and the efficiency of heat engines are constrained by the second law of thermodynamics. The first law of thermodynamics asserts that the energy of the cosmos remains constant, despite the fact that energy may be transferred between systems but neither generated nor destroyed.

2. Give examples of the second law of thermodynamics.

Spontaneously the heat transfer occurs from hot to cold and not from cold to hot. The car’s brake converts the kinetic energy to heat transfer to the environment but its reverse process is impossible. Into the vacuum, the bust of the gas chamber quickly expands to uniformly fill every part of the chamber. Consider what occurs when a rock is dropped and lands on the ground. As the rock falls, its original potential energy transforms into kinetic energy. When a rock collides with the ground, the energy is converted into internal energy of the rock and the ground at the area of contact; molecules move quicker and the temperature rises slightly.

3. In an open system does the thermodynamics law apply?

The second law of thermodynamics is universal and valid without expectations, in an open and closed system, in the non-equilibrium and equilibrium, and in the inanimate and animate system – that is in all space and time scale, useful energy is dissipated in heat and entropy is generated.

4. What is the significance of the second law of thermodynamics?

If you've ever wondered why, when two objects of different temperatures come into contact, thermal energy always flows from the warmer to the cooler, or why, when you start with a glass of room temperature water, some of it never cools and freezes while the rest warms and boils, the second law of thermodynamics can help.

If a glass of room temperature water is spontaneously divided into cool and warm water – or perhaps ice and steam – energy may be saved. That is, the first law does not rule out the possibility of a system at equilibrium at one temperature dividing into a non-equilibrium state in which half of the system warms and the other cools.

This law's importance is that it tells us that any suggested method that would break this condition may be rejected as impossible, without even looking into the details of the process.

5. What is referred to as the Perpetual Motion Machine of 2nd Kind or PMM2?

Perpetual motion machines of the second sort are machines that defy the second law of thermodynamics by continually absorbing heat energy from a single thermal reservoir and totally converting the absorbed heat energy to work energy.

Such machines will have 100% efficiency, or we may argue that perpetual motion machines of the second sort will have better efficiency than the ideal Carnot cycle, which is impossible in my opinion.

As a result, we may conclude that perpetual motion machines of the second sort do not exist since they contradict the second law of thermodynamics.

6. Predict the Second Law of Thermodynamics.

The second law of thermodynamics states that the entire universe entropy as an isolated system will always increase over time. The change in the entropy in the universe can never be a negative state, the second law of thermodynamics.

7. Give examples of the Second Law of Thermodynamics.

Spontaneously the heat transfer occurs from hot to cold and not from cold to hot. The car’s brake converts the kinetic energy to heat transfer to the environment but its reverse process is impossible. Into the vacuum, the bust of the gas chamber quickly expands to uniformly fill every part of the chamber.

8. In an open system does the Thermodynamics Law Apply?

In universal, the second law of thermodynamics and valid without expectations, in an open and closed system in the non-equilibrium and equilibrium in the inanimate and animate system that is in all space and time scale useful energy is dissipated in heat and entropy is generated.