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Introduction to Thermodynamics

Thermodynamics is said to be a branch of physics that deals with heat, work, and temperature and their relation with the energy and radiation and physical properties of matter. The behaviour that is of these quantities is governed by the four laws that are of thermodynamics which convey a quantitative description using measurable macroscopic quantities in physics. But these all can also be explained in terms of microscopic constituents by statistical mechanics. The phenomenon of thermodynamics applies to a wide variety of topics in science and engineering, especially in physical chemistry, chemical engineering and mechanical engineering as well in other complex fields such as meteorology. Here, we will discuss thermodynamics in detail.


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Origin of Thermodynamics 

Before 1798, people were not aware of utilising heat as the source of energy. After that, a British military engineer, Count Rumford, noticed the numerous amounts of heat generated in the boring of cannon barrels. He also identified that the heat generated from the boring cannon barrels are proportional to the work done in turning a blunt boring tool. His observation turned into the foundation of thermodynamics. The concept of the heat-engine cycle and the principle of reversibility was introduced by the French military engineer Sadi Carnot in 1824. But he failed to be concerned about the limitations and the maximum work that can be obtained from a steam engine with a high temperature.  

Later, a German mathematician and physicist, Rudolf Clausius, developed the ideas of  Sadi Carnot and stated the first and second laws of thermodynamics. During the 19th century, the concept of thermodynamics increased rapidly and increased the performance of steam engines and the application of thermodynamics was increased in all physical and biological systems.


Laws of Thermodynamics and Limitations 

The four important laws of thermodynamics and their limitations are explained below

1. First Law Thermodynamics

Law of Conservation of Energy states that energy can neither be created nor can it be destroyed. Energy can only be transferred or changed that too from one form to another. For example, we can say that turning on a light would seem to produce energy, however, it is the electrical energy which is converted.

A way of expressing the first law of thermodynamics is that any change which is in the internal energy denoted by ∆E of a system is given by the sum of the heat that is denoted by q that flows across its boundaries and the work (w) done on the system by the surroundings:

We write it as : ∆E = q + w

This law tells us that there are two kinds of processes: the work process and the heat process that can lead to a change in the internal energy of a system. Since we can see that both heat and work can be measured and quantified so this is the same as saying that any change which is occurring in the energy of a system. In other words, we can say that energy cannot be created or destroyed. If heat usually flows into a system or we can say that the surroundings do work on it then the internal energy increases and the sign q and w are positive. Conversely, we can say that the heat flowing out of the system or work which is done by the system that too on the surroundings will be at the expense of the internal energy and q and w will therefore be negative.

  • Limitations of First Law of Thermodynamics

The first law of thermodynamics does not mention anything about the direction of the flow of heat energy. Also, they did not mention whether the process is spontaneous or not, reversible or not. Practically, the entire heat energy cannot be converted into mechanical energy.

2.The Second Law of Thermodynamics

The second law of thermodynamics says that the entropy of any system which is isolated always increases. The system which is the isolated system spontaneously evolves towards a thermal equilibrium that is the state of entropy which is the maximum of the system. We can say that the entropy of the universe which is of the ultimate isolated system only increases and never decreases.

A simple way in which we can think of the second law of thermodynamics is that of a room. If not cleaned and tidied, then the room will invariably become more messy and disorderly with time – that is regardless of how careful one is to keep it clean. When the room is cleaned then its entropy decreases but the effort to clean it has resulted in an increase in entropy outside the room that exceeds the loss of the entropy.

  • Limitations of Second Law of Thermodynamics

The second law of thermodynamics does not have limitations. But this law is applicable only for the closed system. 

3.The Third Law of Thermodynamics

The entropy that is of a system at absolute zero is typically said to be zero. And we can say that in all cases it is determined only by the number of different ground states it has. Specifically, the entropy of a pure crystalline substance in the perfect order which is at absolute zero temperature is zero. This statement is to hold true if the perfect crystal has only one state with energy that is minimum. 

  • Limitations of Third Law of Thermodynamics

The third law of thermodynamics limits the behaviour of the system because the temperature of the system approaches absolute zero.

4.The Zeroth Law of Thermodynamics

This law identifies the thermal equilibrium and introduces temperature as a tool for identifying equilibrium. According to this law, “we can say that if two systems are in thermal equilibrium with a third system then those two systems themselves are in equilibrium.”

An assembly that is of a very large number of particles whose state can be expressed in terms of pressure and volume and temperature, is known as a thermodynamic system.

  • Limitations of Zeroth Law of Thermodynamics

The zeroth law of thermodynamics is not applicable for all kinds of equilibrium. Other laws cannot be derived from the zeroth law of thermodynamics.

The Thermodynamic System is Said to Be Classified Into the Following Three Systems

(i) Open System: It exchanges both energy and matter with the surrounding.

(ii) Closed System: It exchanges only energy but not matter with surroundings.

(iii) Isolated System: It exchanges neither energy nor matter with the surrounding.

Thermodynamics Notes PDF

The branch of physics which deals with the study of the transformation of heat into other different forms of energy and vice-versa is known as thermodynamics.

The phenomenon of thermodynamics is macroscopic science. It generally deals with bulk systems and does not go into the molecular constitution of the matter.

A collection which is of an extremely large number of molecules or atoms is said to be confined within certain boundaries

such that it has a certain value of pressure denoted by P volume denoted by V and temperature denoted by T is known as a thermodynamic system.

The Thermal Equilibrium

A system of thermodynamics is in a state of equilibrium if the macroscopic variables such as pressure and volume and temperature, mass composition etc. that generally characterise the system do not change in time. In equilibrium that is thermal equilibrium, the temperature of the two systems is said to be equal.

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Fundamental Concepts Of Thermodynamics 

  • Thermodynamic States

The applications of thermodynamic principles completely depend on the system and its surroundings. For example, the system can be a cylinder with gas, movable piston, steam engine, marathon runner etc. Usually, a system will exchange its heat, energy or another form of work with its surroundings. The condition of the system at the given time is called the thermodynamic state.  The changes in the value of the system are completely dependent on their initial and final state. One system cannot follow the path of the other system. In the atmosphere of the earth, the thermodynamic states completely depend on the properties of the components. The thermodynamic state may vary for water and water vapour. 

  • Thermodynamic Equilibrium

Thermodynamic equilibrium is one of the important concepts of thermodynamics. According to thermodynamic equilibrium, no system has the tendency to change the state of a system spontaneously. For example, the gas present inside the cylinder with a moveable piston will remain at equilibrium only if the pressure and temperature inside the cylinder are constant. When the external pressure is imposed on the system, it may change the thermodynamic equilibrium of the system. Usually, no system can be in the equilibrium state, it will adjust according to the changes in the environment. In some systems, it may return to its original state after a small increment, and such a system is said to be a reversible system. 

  • Temperature

If the two objects are brought together to have a thermal contact, then the heat will flow from one object to another, still attaining its equilibrium state. If the transfer of heat between two objects stops, it means that the temperature of the two objects becomes the same. 

The work done by the system is directly proportional to the force applied to the system. The energy of the system refers to the capacity of the system to do certain work. The energy of the system is classified into two types, one is potential energy, and the other is kinetic energy. All the objects will have some potential energy, and the energy developed during the motion of the object is known as kinetic energy. If the object does not have any friction, then the energy of the object is never lost. Albert Einstein also said that it is possible to store the energy in the form of mass and can be converted back into energy through the formula,  E = mc2

Total Internal Energy

Thermodynamics also deals with the macroscopic properties of the materials such as temperature, volume and pressure. The thermal energy of the object will increase as the increase in kinetic energy. The total energy of a system is equal to the sum of internal energy of a system with other forms of energy like kinetic energy, gravitational potential energy etc. 

This article explained the origin of thermodynamics, fundamental concepts of heat and thermodynamics, laws of thermodynamics in detail with their limitations. 

FAQs on Thermodynamics

1. Explain what thermodynamics is.

The phenomenon of thermodynamics is the study of relationships involving heat, and the mechanical work and other aspects of energy transfer that takes place in devices such as refrigerators and the heat pumps as well as the internal combustion engines etc.

2. Explain what is the thermodynamic system in physics.

A thermodynamic system is a body of matter and/or radiation, confined in space by walls that are with defined permeabilities which generally separate it from its surroundings. The surroundings may also include other thermodynamic systems or we can say the physical systems that are not thermodynamic systems.

3. What are the 3 laws of thermodynamics?

Traditionally we can say that thermodynamics has stated three fundamental laws: that is the first law and then the second law and the third law. The first law of thermodynamics states that when energy passes into or out of a system that is as work, heat, or matter then the system's internal energy changes.

4. What is the best definition of heat?

We can say that heat is the form of energy that is transferred between two substances that too at different temperatures. The direction which is of energy flow is from the substance of higher temperature to the substance of temperature which is lower. Heat is said to be measured in units of energy that is usually calories or joules.

5.What is a simple definition of thermodynamics?

Answer: Thermodynamics is a branch of physics, which shows the relationship between work, heat, temperature and energy. The laws of thermodynamics explain how the energy in the system can be converted into energy and how the system can utilize the energy to perform certain tasks.

6.How is thermodynamics used in everyday life?

Answer: Usually, the human body works on the principle of laws of thermodynamics. For example, the sweat from the human body will act as the medium to transfer body heat to the air. When sweating, people gather together in the room, the temperature of the room gets high quickly as the sweat exchanges heat from the body to the room.

7.What is CV in thermodynamics?

Answer: The two common terms used in thermodynamics are CV and CP. The CV represents the specific heat at a constant volume. CP represents the specific heat at constant pressure. The specific heat represents the heat energy required to raise the temperature of a substance by one degree celsius.