## Thermodynamics – Class 11 | Chapter – 12 | Physics Short Notes Series PDF for NEET & JEE

Thermodynamics: Thermodynamics is the branch of physics that deals with the study of the relationship between heat, energy, and work. It is concerned with the behavior of macroscopic systems (e.g., a gas or a mixture of fluids) and their transformations from one state to another, and the laws that govern these transformations.

Thermodynamics is a fundamental theory in the physical sciences, and it has applications in many areas, including engineering, chemistry, materials science, and environmental science. The principles of thermodynamics provide a framework for understanding how energy is converted from one form to another and how it is transferred between systems, as well as the limitations of such conversions. The laws of thermodynamics are considered some of the most important and fundamental laws in all of physics.

## Types of Thermodynamic Equilibriums

There are several types of thermodynamic equilibria, including:

• Thermal equilibrium: When two or more systems are in contact with each other and there is no net transfer of heat between them, they are said to be in thermal equilibrium.
• Mechanical equilibrium: When there is no net force acting on a system, it is said to be in mechanical equilibrium. For example, a gas in a container that is at rest and not being compressed or expanded is in mechanical equilibrium.
• Chemical equilibrium: When the chemical reaction rates in a system are equal and there is no net change in the concentrations of reactants or products, the system is said to be in chemical equilibrium.
• Phase equilibrium: When two or more phases of a substance (such as solid, liquid, or gas) are present in a system and the composition and temperature of each phase are constant, the system is said to be in phase equilibrium.
• Radiative equilibrium: When a system is absorbing and emitting radiation at the same rate, it is said to be in radiative equilibrium.

All of these types of equilibria are important in understanding the behavior of thermodynamic systems, and they are used to develop many of the fundamental principles of thermodynamics.

## Procedure of Thermodynamic

A thermodynamic procedure typically involves the following steps:

• Define the system: This involves defining the boundaries of the system and identifying its properties, such as mass, volume, pressure, temperature, and energy.
• Choose a thermodynamic process: This involves selecting a specific transformation of the system, such as heating, cooling, compression, expansion, or mixing.
• Apply the laws of thermodynamics: This involves using the first, second, and third laws of thermodynamics to analyze the behavior of the system during the chosen process. The laws of thermodynamics describe the relationships between heat, energy, and work, and they provide fundamental principles for understanding the behavior of thermodynamic systems.
• Calculate the thermodynamic quantities: This involves calculating the thermodynamic properties of the system, such as its internal energy, enthalpy, entropy, and free energy. These quantities can be calculated using mathematical formulas based on the laws of thermodynamics.
• Interpret the results: This involves analyzing and interpreting the calculated thermodynamic quantities to understand the behavior of the system during the chosen process. This analysis can provide insights into the efficiency, stability, and performance of the system.

Thermodynamic procedures are used in a wide range of applications, from designing and optimizing energy systems to developing new materials and chemical processes.

## System and the Surroundings of Thermodynamic

In thermodynamics, a system refers to a specific portion of the universe that is being studied, while the surroundings refer to everything outside of the system. The system and surroundings are separated by a boundary, which can be either real or imaginary.

The system can be of different types depending on the context of the study. For example, if we are studying a gas contained in a cylinder, the gas inside the cylinder will be the system, and the cylinder walls and the air outside of the cylinder will be the surroundings.

The system can be further classified as open, closed, or isolated based on the flow of matter and energy across the system boundary:

• Open system: In an open system, both matter and energy can be exchanged with the surroundings. For example, a pot of boiling water on a stove is an open system because heat and water vapor can escape into the surroundings.
• Closed system: In a closed system, energy can be exchanged with the surroundings, but no matter can cross the boundary. For example, a piston-cylinder assembly containing a gas is a closed system because no gas can enter or leave the system, but heat can be added or removed through the cylinder walls.
• Isolated system: In an isolated system, neither matter nor energy can be exchanged with the surroundings. An example of an isolated system is a perfectly insulated container that contains a gas.

The behavior of a system in thermodynamics is determined by the interactions between the system and the surroundings, which can be described using the laws of thermodynamics. The system and surroundings are integral to the understanding of thermodynamics, and a proper understanding of their interactions is essential to applying thermodynamics in practical applications.

### Thermodynamics: Internal Energy

In thermodynamics, the internal energy of a system is the sum of all the microscopic energies of the particles that make up the system, including their kinetic and potential energies. It is denoted by the symbol U and is a state function, which means that it depends only on the current state of the system, not on how it got there.

The internal energy of a system can be changed by adding or removing heat or doing work on or by the system. The first law of thermodynamics states that the change in internal energy of a system is equal to the heat added to or removed from the system plus the work done on or by the system:

ΔU = Q – W

where ΔU is the change in internal energy, Q is the heat added to or removed from the system, and W is the work done on or by the system.

The internal energy of a system can be expressed in different forms, depending on the context of the problem. For example, it can be expressed as a function of temperature, pressure, and volume using thermodynamic equations of state, such as the ideal gas law.

The internal energy is an important concept in thermodynamics because it is a measure of the total energy of a system, and it is used to calculate other thermodynamic properties, such as enthalpy and entropy. The internal energy of a system also plays a crucial role in determining the direction and extent of thermodynamic processes.

### Thermodynamics: Work (Pressure-volume Work)

In thermodynamics, work refers to the transfer of energy to or from a system through a mechanical process, such as by compression or expansion. Pressure-volume work is one type of work that occurs when a system undergoes a change in volume due to an external force, such as the compression or expansion of a gas in a cylinder.

The pressure-volume work, denoted by the symbol W, can be calculated using the following equation:

W = -PΔV

where P is the pressure of the system and ΔV is the change in volume. The negative sign indicates that work is done on the system if the volume decreases (compression), and work is done by the system if the volume increases (expansion).

The pressure-volume work is a form of mechanical work and is related to the force and displacement of the system. It is a path function, which means that it depends on the specific path taken by the system during the process.

The pressure-volume work is an important concept in thermodynamics because it is a way to transfer energy between a system and its surroundings. In addition, it is used to calculate other thermodynamic properties, such as the internal energy and enthalpy of a system, and it plays a crucial role in many practical applications, such as in the design of engines and power generation systems.

### Enthalpy (H)

In thermodynamics, enthalpy (H) is a thermodynamic property that describes the total heat content of a system. It is defined as the sum of the internal energy (U) of the system and the product of the pressure (P) and volume (V) of the system:

H = U + PV

Enthalpy is a state function, which means that its value depends only on the current state of the system, not on how it got there. This property is used to describe the heat exchange that takes place during a process, such as a chemical reaction, phase change, or physical transformation.

Enthalpy can be used to predict whether a process is exothermic or endothermic. If the enthalpy of the products is lower than the enthalpy of the reactants, the process is exothermic, meaning that heat is released into the surroundings. If the enthalpy of the products is higher than the enthalpy of the reactants, the process is endothermic, meaning that heat is absorbed from the surroundings.

Enthalpy is an important concept in many branches of science and engineering, particularly in chemical engineering, where it is used to describe chemical reactions and phase changes in industrial processes. It is also used in the design and analysis of thermal systems, such as power plants, refrigeration systems, and air conditioning systems.

### Spontaneity

In thermodynamics, spontaneity refers to the tendency of a system to move towards a state of lower energy and greater stability without external influence. A spontaneous process is one that occurs naturally and without the need for energy input or external intervention.

Spontaneity is determined by the change in free energy (ΔG) of a system. If ΔG is negative, the process is spontaneous, meaning that it will proceed without the need for additional energy. If ΔG is positive, the process is non-spontaneous and will require energy input to proceed. If ΔG is zero, the process is at equilibrium, meaning that the system is in a stable state where the rate of the forward and reverse reactions are equal.

Spontaneity is not the same as speed, as a spontaneous process can occur slowly or quickly depending on the nature of the system and the conditions under which the process occurs. For example, the rusting of iron is a spontaneous process that occurs slowly over time, while the explosion of dynamite is a spontaneous process that occurs very quickly.

Spontaneity is an important concept in thermodynamics, as it helps to predict the direction and outcome of chemical reactions and physical processes. It is also a key factor in the design and operation of energy conversion systems, such as engines and power plants.

### Entropy (S)

In thermodynamics, entropy (S) is a measure of the disorder or randomness of a system. It is a state function that describes the distribution of energy within a system and the number of possible microstates that are available to the system at a given energy level.

Entropy can be thought of as a measure of the amount of energy that is unavailable to do work. When energy is transferred or converted from one form to another, some of it is always lost as unusable energy, which increases the entropy of the system.

The change in entropy of a system (ΔS) is related to the heat transfer (Q) that occurs during a process, as described by the following equation:

ΔS = Q/T

where T is the absolute temperature of the system. This equation is known as the Clausius inequality, and it states that the entropy of a closed system can never decrease over time. This is known as the second law of thermodynamics.

Entropy plays an important role in many areas of science and engineering, including thermodynamics, chemistry, physics, and information theory. It is used to predict the direction and outcome of chemical reactions and physical processes, and it is a key factor in the design and operation of energy conversion systems. In information theory, entropy is used to quantify the amount of information contained in a message or signal.

 JOIN OUR TELEGRAM CHANNELS Biology Quiz & Notes Physics Quiz & Notes Chemistry Quiz & Notes 