THERMODYNAMICS

 

The word ‘thermodynamics’ is derived from two words: thermo and dynamics. ‘Thermo’ stands for heat while ‘dynamics’ is used in connection with a mechanical motion which involves ‘work’. 

Broadly speaking, thermodynamics is a branch of science that deals with heat, work and temperature, and their relation to energy, radiation and physical properties of matter. It explains how thermal energy (heat energy) is converted to other forms of energy and how matter is affected by this process.

Different Branches of Thermodynamics:

• Classical Thermodynamics
• Statistical Thermodynamics
• Chemical Thermodynamics
• Equilibrium Thermodynamics

In classical thermodynamics, temperature and pressure are taken into consideration, which helps us to calculate other properties and predict the characteristics of the matter undergoing the process.

Chemical thermodynamics is the study of how work and heat relate to each other in chemical reactions

and in changes of states.

THERMODYNAMIC TERMS AND BASIC CONCEPTS: 

To study the basic concepts of thermodynamics it is important to study a few terms and definitions which must be understood clearly.

Thermodynamic Systems:

A system is that part of the universe which is under thermodynamic study and the rest of the

universe is surroundings. The real or imaginary surface separating the system from the

surroundings is called the boundary

There are three types of systems:

Open System –

 In an open system, the mass and energy both may be transferred between the system and surroundings. A steam turbine is an example of an open system.

Closed System – 

In the closed system, the transfer of energy takes place but the transfer of mass doesn’t take place. Refrigerator, compression of gas in the piston assembly, etc., are examples of closed systems.

Isolated System – 

An isolated system cannot exchange energy and mass with its surroundings. The universe is considered an isolated system.

THERMODYNAMIC PROCESS:

The change of thermodynamic state from one condition to another condition ( change in temperature or pressure) is called thermodynamic process. One example of a thermodynamic process is increasing the temperature of a fluid while maintaining a constant pressure.

REVERSIBLE PROCESS:

A reversible process for a system is defined as a process that, once having taken place, can be reversed, and in so doing leaves no change in either the system or surroundings. In reality, there are no truly reversible processes. One way to make real processes approximate reversible process is to carry out the process in a series of small or infinitesimal steps.

For example, transferring heat across a temperature difference of 0.00001 °F "appears" to be more reversible than for transferring heat across a temperature difference of 100 °F. Therefore, by cooling or heating the system in a number of infinitesimally small steps, we can approximate a reversible process.

IRREVERSIBLE PROCESS

An irreversible process is a process that cannot return both the system and the surroundings to their original conditions. That is, the system and the surroundings would not return to their original conditions if the process was reversed. 

For example, an automobile engine does not give back the fuel it took to drive up a hill as it coasts back down the hill.

Isothermal Process

An isothermal process is a thermodynamic process that takes place at a constant temperature. It means that an isothermal process occurs in a system where the temperature remains constant. However, to keep the temperature of the system constant, heat must be transferred into the system or shifted out of the system.

In simple terms, in the isothermal process: T = constant. This implies, the change in temperature will be zero i.e., ΔT=0

Examples:

Melting and Evaporation, etc. 

Working in the refrigerator is an isothermal process. The temperature of the surroundings changes irrespective of changes in the internal temperature of the refrigerator. Excess heat is removed and transmitted to the surrounding.

Adiabatic Process:

An adiabatic process is a thermodynamic process that can take place without any heat transfer between a system and its surrounding. Here, neither heat nor energy is not transferred into or out of the system. Therefore, in an adiabatic process, the only way the energy transfer takes place between a system and its surroundings is the work. 

Examples:

1. Release of air from a pneumatic tyre.

 A pneumatic tire consists of an outer rubber layer, an inner chamber that contains compressed air and a tread pattern. This type of tire works by utilizing the air-filled chamber to provide cushioning and absorb shocks. Under a load, the tire compresses the air inside, distributing the weight evenly and reducing the impact on surfaces. The design allows for a smooth, stable ride, while the tread pattern on the tire provides grip and traction. The tire's flexibility and the pressurized air inside enable it to adapt to different terrains and surfaces. When a tyre bursts, the sudden release of the high-pressure air inside the tyre causes the air to rapidly expand. This rapid expansion of the gas occurs without any heat transfer to or from the surroundings, as the process happens too quickly for significant heat exchange to take place.