The second law of thermodynamics

The first law of thermodynamics asserts that the universe’s energy stays constant; energy is transferred among systems but not produced or destroyed.

The first law of thermodynamics offers information about the amount of energy transmitted, but this does not provide information about the direction of the transfer of energy. The first law seems unable to anticipate whether a uniformly heated metal bar will become a warmer place at one end and calmer at another. The law could only state that there will still be an energy balance even if the process happens. The second law of thermodynamics determines the efficiency of any strategy. Either it must fulfill the first or second rules of thermodynamics for a function to occur.

The Second Law of Thermodynamics

According to the second law of thermodynamics, any naturally occurring activity increases the universe’s entropy. The law says that an isolated system’s entropy could never decrease considerably in layman’s terms.

The overall entropy system and surroundings stay unchanged in some circumstances in which the system is in thermodynamic equilibrium and going through a reversible reaction. The law of increasing entropy is another name for the second law.

According to the second law, it is not possible to transform thermal energy to mechanical energy at 100% efficiency. For instance, the gas is warmed in an engine to raise its pressure to move a piston. Even when the piston moves, specific heat is left in the gas, which can’t be used for anything else. Heat is wasted and should be discarded.

In this situation, waste heat is eliminated by expelling in used air and fuel mixture to the atmosphere or, in the case of an automobile engine, via transmitting it to a heat sink. Furthermore, heat generated by friction must be eliminated from the system because it is useless.

The equation for the Second Law Of Thermodynamics state  simply;

ΔSuniv > 0

Where ΔSuniv is the change in the universe’s entropy.

Entropy measures a system’s random measurement of power or chaos within a closed system. It can be regarded as a quantitative metric for describing energy quality.

However, there are only just a few causes that cause a closed system’s entropy to rise. In a closed system, heat is exchanged only with the environment, whereas the mass remains unchanged. This shift in heat content disrupts the system, raising the entropy of a system.

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

Statements of the second law of thermodynamics

There are two statements of the second law of thermodynamics. 

• Kelvin-Planck Statement
• Clausius Statement

Kelvin- Planck Statement

According to this statement, it is impossible for a heat engine to convert all absorbed heat into work while taking heat from only one reservoir. In another word, a 100 % efficient engine can’t be produced. 

Clausius’s Statement

It’s challenging to build a gadget that works in a cycle and transfers heat from the colder body to a warmer one without spending any energy. Moreover, power would not naturally transfer from low-temperature to higher-temperature components. It’s vital to understand that we’re talking about energy transfer on a net basis. Energy can be transferred from a cold object to a hot thing via energetic particles and electromagnetic radiation.

Regardless of the outcome, the net transfer would be from a hot object to a cold thing. Any form of work is required to move the net energy to a hot object. In other words, unless such an external source drives such a compressor, the refrigerator would not function. 

The heat pump and the refrigerator use Clausius’s statement.

Clausius and Kelvin’s statements are equal, which means that a device that violates Clausius’s statement also simultaneously violates Kelvin’s statement & Concerning such statements, a French physicist recognized as the “father of thermodynamics,” Nicolas Léonard Sadi Carnot, tried to introduce the application of the second law of thermodynamics. Moreover, he emphasizes the importance of using caloric theory to state the second law of thermodynamics. Caloric (self-repellent fluid) is related to heat, but Carnot noticed that caloric was lost even during the motion cycle.

Second-Generation Perpetual Motion Machine (PMM2)

The second type of perpetual motion machine functions while coping with a single heat source (PMM2). The second category of perpetual motion machines violates the second law of thermodynamics.

A heat engine with at least two thermal reservoirs at different temperatures should create work in a cycle. It can generate motive power (i.e., work) as soon as a temperature variation. If indeed the bodies to which it transforms have finite heat capacity, the engine will make things until the temperature of the two bodies is evenly distributed.

The Second Law of Thermodynamics Examples

• To extract 500 J at a low temperature reservoir, a heat-engine does 400 J work. Find how much heat is absorbed from a high temperature reservoir?

           Given work done    W = 400 J

            Heat removed QC = 500 J

             From energy equation of heat engine

QH = W + QC

   QH = 400 J + 500 J

              QH = 900 J

Heat absorb from higher temperature reservoir is 900 J.

• A heat engine works on temperature 400K and absorbs The heat 2000 kJ from a high temperature reservoir.  Calculate the change in entropy of the heat engine. 

              Given absorbed heat  dQ = 2000 kJ

               Temperature of engine T = 400K

Change In Entropy (ΔS)= dQ/T

ΔS = 2000kJ400K= 5kJ/K

  Change in entropy is equal to 5 kJ/K

Conclusion

The application of the second law of thermodynamics deals with power quality. It means that even a more significant proportion of energy is wasted since it is carried or processed. Applying the second law of thermodynamics also suggests that each isolated system naturally degrades towards a more chaotic state.