NEET Notes: Thermodynamics

NEET Notes: Thermodynamics

Introduction to Thermodynamics

Thermodynamics is the branch of physics that deals with the study of heat, energy, and the work done by or on a system. It explains the relationship between heat and other forms of energy, and how energy is transferred and transformed in various processes. For NEET aspirants, understanding thermodynamics is crucial as it forms the basis of many natural phenomena and is vital for solving related problems in the exam.

Basic Concepts of Thermodynamics

• System: A system is the part of the universe that is being studied, and everything outside it is called the surroundings.
• Surroundings: The rest of the universe outside the system is referred to as the surroundings.
• Boundary: The real or imaginary surface separating the system from its surroundings is known as the boundary.
• State: The state of a system is defined by properties such as pressure, volume, and temperature.
• Process: A process is the transition from one state to another.

Types of Systems

• Closed System: A system that can exchange energy but not matter with its surroundings.
• Open System: A system that can exchange both energy and matter with its surroundings.
• Isolated System: A system that does not exchange either energy or matter with its surroundings.

First Law of Thermodynamics

The first law of thermodynamics, also known as the law of energy conservation, states that energy cannot be created or destroyed, only converted from one form to another. Mathematically, it is expressed as:

ΔU = Q - W

Where ΔU is the change in internal energy of the system, Q is the heat absorbed by the system, and W is the work done by the system on its surroundings.

Work and Heat in Thermodynamic Processes

In thermodynamics, work refers to the energy transferred when a force is applied over a distance, while heat is the energy transferred due to temperature differences. Both work and heat are essential in understanding how energy is transferred between the system and its surroundings during various processes.

Types of Thermodynamic Processes

Isothermal Process

An isothermal process occurs at a constant temperature. During an isothermal process, the system absorbs or releases heat without changing its temperature. This process is common in processes involving gases in thermodynamic cycles.

Adiabatic Process

An adiabatic process occurs without any heat exchange between the system and its surroundings. In this process, the change in internal energy of the system is equal to the work done by or on the system. The temperature of the system changes as a result of work done.

Isochoric Process

An isochoric process occurs at constant volume. During this process, no work is done, and any heat added to the system increases its internal energy, which increases the temperature of the system.

Isobaric Process

An isobaric process occurs at constant pressure. In this process, the system absorbs or releases heat, and the volume of the system changes while maintaining constant pressure.

Second Law of Thermodynamics

The second law of thermodynamics states that the total entropy (disorder) of an isolated system always increases over time. This law introduces the concept of irreversibility and explains why certain processes, such as heat flow from hot to cold, are spontaneous. It also leads to the concept of entropy as a measure of the randomness or disorder in a system.

Entropy

Entropy is a measure of the disorder or randomness of a system. In thermodynamics, it is defined as:

ΔS = Q/T

Where ΔS is the change in entropy, Q is the heat absorbed by the system, and T is the temperature at which the heat is absorbed. The second law of thermodynamics implies that the entropy of the universe is constantly increasing.

Third Law of Thermodynamics

The third law of thermodynamics states that the entropy of a system approaches zero as the temperature approaches absolute zero (0 K). At absolute zero, the system is in a perfect order, and no further decrease in entropy is possible.

Thermodynamic Potentials

Thermodynamic potentials are functions that are used to describe the energy of a system. These include:

• Internal Energy (U): The total energy contained within the system.
• Enthalpy (H): The total heat content of a system, defined as H = U + PV, where P is pressure and V is volume.
• Helmholtz Free Energy (A): A potential that is useful when dealing with systems at constant volume and temperature, defined as A = U - TS, where T is temperature and S is entropy.
• Gibbs Free Energy (G): A potential that is useful for systems at constant temperature and pressure, defined as G = H - TS.

Applications of Thermodynamics

Heat Engines

Heat engines operate on the principles of thermodynamics, converting heat energy into mechanical work. These engines, such as the Carnot engine, follow a cyclic process and are governed by the laws of thermodynamics. The efficiency of a heat engine depends on the temperature difference between the hot and cold reservoirs.

Refrigerators and Heat Pumps

Refrigerators and heat pumps use the second law of thermodynamics to transfer heat from a cold reservoir to a hot one. They require work input to transfer heat against its natural flow, from lower to higher temperature.

Thermodynamics in Biological Systems

In biological systems, thermodynamics plays a critical role in understanding processes such as respiration, digestion, and metabolism. Energy transfer and transformation are essential in sustaining life and maintaining cellular processes in living organisms.

Conclusion

Thermodynamics is a fundamental branch of physics that provides valuable insights into how energy is transformed and transferred. The laws of thermodynamics are applicable across a wide range of systems, from simple gases to complex biological processes. Mastering thermodynamics is essential for NEET aspirants, as it forms the foundation for various topics in physical chemistry and physics.