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Created by: Team Physics -, Last Updated: April 25, 2024


What is Thermodynamics?

Thermodynamics is a branch of physics that studies the relationships and conversions between heat and other forms of energy. It examines how energy transformations are governed by certain laws, influencing various physical processes and systems.

Thermodynamics Formula

A fundamental and commonly used formula in thermodynamics is the First Law of Thermodynamics, which is expressed as:



  • ΔU represents the change in internal energy of the system.
  • Q is the heat added to the system.
  • W is the work done by the system.

This formula encapsulates the principle of energy conservation within a thermodynamic system, indicating that any increase in the internal energy (ΔU) of the system is the result of the net heat added to the system (Q) minus the work done by the system on its surroundings (W).

Examples of Thermodynamics

  1. Refrigerators: Utilize thermodynamics to extract heat from inside to keep food cold.
  2. Steam Engines: Use heat from burning coal to create steam that moves pistons and produces mechanical work.
  3. Air Conditioners: Extract heat from an interior space and release it outside to cool the area.
  4. Human Body: Manages internal temperature through metabolic heat production and dissipation.
  5. Thermal Power Plants: Convert heat from burning fuels into electrical energy via steam turbines.
  6. Automobile Engines: Transform chemical energy from fuel into mechanical energy through combustion.
  7. Heat Pumps: Move heat from a cooler area to a warmer one to provide heating or vice versa for cooling.
  8. Boilers: Heat water to create steam for heating buildings or powering engines.
  9. Solar Panels: Convert solar energy into heat or electrical energy, demonstrating energy conversion.
  10. Chemical Reactions: Many endothermic and exothermic reactions involve heat transfer as part of reaction processes.
  11. Evaporative Coolers: Use the evaporation of water to cool air through the absorption of heat, which is a practical application of latent heat.
  12. Geothermal Systems: Utilize the Earth’s heat for direct heating or for generating electricity.
  13. Incinerators: Burn waste materials to reduce volume and mass, converting chemical energy in the waste into thermal energy.
  14. Stirling Engines: Operate on the cyclic compression and expansion of air or other gases at different temperatures, converting heat energy into mechanical work.

Types of Thermodynamics

Types of Thermodynamics

1. Classical Thermodynamics

Classical thermodynamics focuses on the macroscopic behavior of energy and materials without considering atomic details. It is based on the laws of thermodynamics, which define relationships between heat, work, temperature, and energy in systems.

  • Example: Calculating the efficiency of heat engines such as steam turbines or refrigerators.
  • Equation: First Law of Thermodynamics, ΔU=QW, where ΔU is the change in internal energy, Q is heat added, and W is work done by the system.

2. Statistical Thermodynamics

Statistical thermodynamics bridges microscopic atomic and molecular behavior with macroscopic observations using statistical methods to explain thermodynamic phenomena, focusing on the behavior of systems at the particle level.

  • Example: Describing the heat capacity of gases by accounting for molecular motion and degrees of freedom.
  • Equation: Boltzmann distribution, Pi​=ZeEi​/kBT​, where Pi​ is the probability of a system being in a state with energy Ei​, kB​ is the Boltzmann constant, T is temperature, and Z is the partition function.

3. Chemical Thermodynamics

Chemical thermodynamics applies thermodynamic principles to chemical reactions and energy changes, emphasizing the study of reaction energies and equilibrium.

  • Example: Predicting the direction of chemical reactions and the equilibrium position based on Gibbs free energy.
  • Equation: Gibbs free energy, ΔGHTΔS, where ΔG is the change in Gibbs free energy, ΔH is the change in enthalpy, ΔS is the change in entropy, and T is temperature.

4. Equilibrium Thermodynamics

This branch deals with systems at thermodynamic equilibrium, where macroscopic properties do not change over time. It involves the study of energy distributions and phase transitions under equilibrium conditions.

  • Example: Determining the melting point of ice or the boiling point of water under different pressures.
  • Equation: Clapeyron equation, dTdP​=TΔVΔH​, which describes how the pressure P of a system changes with temperature T during a phase change, where ΔH and ΔV are the changes in enthalpy and volume, respectively.

5. Non-equilibrium Thermodynamics

Non-equilibrium thermodynamics examines systems away from equilibrium, which is essential for understanding real-world systems where energy and matter transfers are unbalanced.

  • Example: Exploring the entropy production in living organisms or the behavior of rapidly changing weather systems.
  • Equation: Fourier’s law of heat conduction, q˙​=−kT, where ˙q˙​ is the heat flux, k is the thermal conductivity, and ∇T is the temperature gradient.

How to Use Thermodynamics?

1. Engineering Applications

  • Energy Systems: Design and optimize power plants, engines, and refrigerators to efficiently convert and use energy.
  • HVAC Systems: Apply thermodynamic principles to develop heating, ventilation, and air conditioning systems that maintain desired environmental conditions efficiently.
  • Material Science: Use thermodynamics to understand and predict material behavior under different temperatures and pressures.

2. Environmental Management

  • Climate Studies: Model and predict climate patterns and energy transfers in the atmosphere using thermodynamic equations.
  • Renewable Energy: Design systems for solar panels, wind turbines, and geothermal energy extraction based on thermodynamic efficiency and energy conversion rates.

3. Industrial Processes

  • Chemical Manufacturing: Optimize chemical reactions and processes by understanding the energy changes and equilibria described by chemical thermodynamics.
  • Food Industry: Control processes like pasteurization, freezing, and drying, where heat and mass transfer are crucial.

4. Automotive Sector

  • Engine Design: Improve the efficiency of combustion engines by analyzing the thermodynamic cycles and minimizing energy losses.
  • Battery Management: Use thermodynamics to enhance battery performance and safety in electric vehicles, focusing on thermal management.

5. Research and Development

  • Innovative Technologies: Develop new materials and technologies like superconductors and nanomaterials by understanding their thermodynamic properties.
  • Biotechnology: Apply bio thermodynamics to study metabolic processes and energy transformations in biological systems.

6. Everyday Applications

  • Cooking: Understand how heat transfer works in cooking processes like boiling, baking, or frying.
  • Home Energy Use: Apply basic thermodynamic principles to improve home insulation and energy use efficiency.

7. Educational Tools

  • Teaching: Use thermodynamic concepts to teach principles of physics and chemistry, making abstract concepts tangible through real-world applications.
  • Simulations and Models: Create simulations to predict the outcomes of thermodynamic processes, useful in educational settings and research.

Importance of Thermodynamics

Thermodynamics is a critical discipline within physics and engineering that has wide-reaching implications across numerous fields. Here’s why thermodynamics is so important:

1. Understanding Natural Processes

Thermodynamics helps explain natural phenomena at both macroscopic and microscopic levels. It provides insights into the workings of everything from atmospheric dynamics and ocean currents to biological processes and the fundamental operations of the universe.

2. Energy Conversion and Management

It is essential for the efficient design, operation, and analysis of systems that convert energy from one form to another, such as engines, power plants, and refrigerators. Thermodynamics enables the optimization of these systems for more sustainable energy use and increased performance.

3. Environmental Impact

Thermodynamics plays a pivotal role in environmental engineering and sustainability studies. It helps assess the impact of energy usage on the environment, facilitating the development of technologies that reduce waste and improve energy efficiency.

4. Advancements in Technology

The principles of thermodynamics are fundamental to developing new materials and technologies, including advances in renewable energy sources, automotive industry improvements, and innovative solutions in electronics and materials science.

5. Chemical Industry

In the chemical industry, thermodynamics is crucial for the design and operation of processes that involve chemical reactions, separation processes, and the production of compounds. It helps in predicting reaction outcomes, energy needs, and material properties under various conditions.

6. Economic Efficiency

By improving the efficiency of thermal systems, thermodynamics directly influences economic efficiency in manufacturing, power generation, heating, and cooling systems. This reduces costs and energy consumption, leading to more economically viable operations.

7. Education and Research

Thermodynamics is a foundational subject in science and engineering education, enabling students and researchers to apply its concepts to a variety of complex problems and innovations.

8. Medical and Health Sciences

In the field of biotechnology and medical sciences, thermodynamics helps in understanding metabolic processes and the physiochemical aspects of body functions, contributing to medical diagnostics, drug design, and other therapeutic practices.

Properties of Thermodynamics

1. Temperature

Temperature is a measure of the average kinetic energy of the particles in a substance. It’s fundamental for describing heat transfer between systems and is measured in degrees Celsius (°C), Kelvin (K), or Fahrenheit (°F).

2. Pressure

Pressure is the force exerted per unit area by the particles of a substance. It is a critical factor in determining the behavior of gases and liquids and is measured in pascals (Pa) or atmospheres (atm).

3. Volume

Volume is the space occupied by a substance. Changes in volume can significantly affect pressure and temperature of a system, especially in gaseous states.

4. Internal Energy

Internal energy is the total energy contained within a system, including kinetic and potential energies of particles. It changes with heat transfer and work done by or on the system.

5. Entropy

Entropy measures the disorder or randomness in a system. It is a central concept in the Second Law of Thermodynamics, indicating that systems tend to move towards more disordered states.

6. Enthalpy

Enthalpy is the total heat content of a system at constant pressure. It is used especially in scenarios involving heat transfer in chemical reactions and phase changes.

7. Specific Heat Capacity

Specific heat capacity is the amount of heat required to change the temperature of a unit mass of a substance by one degree Celsius. It varies among different materials and is crucial for thermal management.

8. Gibbs Free Energy

Gibbs free energy is a thermodynamic potential that measures the maximum reversible work that may be performed by a thermodynamic system at constant temperature and pressure. It is particularly useful in chemical thermodynamics to predict the direction of chemical reactions.

9. Helholtz Free Energy

Helmholtz free energy is a thermodynamic potential that measures the useful work obtainable from a closed thermodynamic system at a constant temperature. It’s valuable for understanding systems that perform work at stable temperatures.

Laws of Thermodynamics

Laws of Thermodynamics

Thermodynamics is governed by several fundamental laws that describe the behavior of energy in various systems. Here’s a detailed look at these laws along with relevant equations and formulas:

Zeroth Law of Thermodynamics

Principle: The Zeroth Law establishes a basis for temperature measurement, stating that if two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.

Implication: This law allows for the definition of temperature in a practical sense and is the foundation of temperature measurement.

First Law of Thermodynamics (Law of Energy Conservation)

Principle: Energy cannot be created or destroyed in an isolated system. The change in the internal energy of a system is equal to the heat added to the system minus the work done by the system on its surroundings.

Equation: ΔU = QW Where:

  • ΔU is the change in internal energy,
  • Q is the heat added to the system (positive if added, negative if removed),
  • W is the work done by the system (positive if done by the system, negative if done on the system).

Second Law of Thermodynamics

Principle: The total entropy of an isolated system can never decrease over time. It remains constant if all processes are reversible and increases if they are irreversible. This law also states that heat cannot spontaneously transfer from a colder body to a hotter body.

Equations: For a reversible process, ΔS=∫dQᵣₑᵥ/T​​ Where:

  • S is the change in entropy,
  • dQᵣₑᵥ​ is the infinitesimal amount of heat added reversibly,
  • T is the absolute temperature.

For spontaneous processes in isolated systems, ΔS>0

Third Law of Thermodynamics

Principle: As the temperature of a system approaches absolute zero, the entropy of the system approaches a constant minimum.

Implication: This law implies that it is impossible to reach absolute zero in a finite number of operations, and as temperature approaches absolute zero, the system displays less and less energy.

Mathematical Formulation: limₜ→₀S=S₀​ Where S₀ is typically zero for perfectly crystalline substances.

Difference Between Mechanics and Thermodynamics

DefinitionMechanics is the branch of physics that deals with the motion of bodies under the action of forces.Thermodynamics is the study of the relationships between heat, work, temperature, and energy in a system.
FocusFocuses on the forces and their effects on motion.Focuses on energy transformations and the state properties of systems.
LawsNewton’s laws of motion and principles of conservation of momentum are central.Laws of thermodynamics, which include energy conservation, entropy, and absolute temperatures, are central.
ApplicationsApplied in studying objects from sub-atomic particles to astronomical objects in motion.Applied in understanding and designing heat engines, refrigerators, and all manners of thermal systems.
QuantitiesDeals primarily with force, mass, acceleration, displacement, and velocity.Deals with temperature, heat, internal energy, entropy, and enthalpy.
EquationsKey equations include F=ma (Newton’s second law) and equations of motion.Key equations include the first and second laws of thermodynamics (ΔU=QW, ΔS≥0).
Nature of StudyOften involves deterministic approaches where the outcomes are predictable based on initial conditions.Often involves statistical approaches, especially in systems involving large numbers of particles.
Practical ExamplesDesign of structures, vehicles, machines, and studying planetary motions.Design of HVAC systems, power plants, engines, and understanding biological and chemical processes.


What is the principle of thermodynamics?

Thermodynamics revolves around the study of energy transfers and transformations in physical and chemical processes, emphasizing heat, work, temperature, and entropy.

What is the first law of thermodynamics for dummies?

The first law states that energy in a closed system is constant; it cannot be created or destroyed, only converted from one form to another.

What is the 5th law of thermodynamics?

There is no officially recognized 5th law of thermodynamics; the discipline traditionally includes only four fundamental laws.

Does the human body obey the laws of thermodynamics?

Yes, the human body obeys all thermodynamic laws, including energy conservation and entropy changes, through metabolic and physiological processes.

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