Thermodynamics

1.0What is Thermodynamics?

Thermodynamics is the branch of science that deals with the energy changes taking place in all physical and chemical processes, but Chemical thermodynamics is the branch of thermodynamics that deals with the study of energy changes taking place in chemical processes.

To simplify thermodynamics, a clear boundary is established around a system, encompassing everything within it. The surroundings are everything outside this boundary. This setup helps describe the movement and transfer of energy across the system's boundaries. The system and its surroundings constitute the "universe" in thermodynamics.

2.0Thermodynamic Terms

System: A system is defined as a specific part of the universe or a specified portion of matter that is under experimental investigation.

• Surroundings: The rest of the universe, excluding the system, is called the surroundings.
• Universe: The universe is the sum of the system and its surroundings.
• Universe= System + Surroundings
• Boundary: Anything that separates the system from its surroundings is called a boundary.

Surroundings

The surroundings of a thermodynamic system include everything external to the system that can interact with it. Based on the nature of the interaction between a system and its surroundings, thermodynamic systems can be classified into three types:

• Open System: An open system can exchange energy and matter with its surroundings. This type of system is not isolated and allows for transferring heat, work, and mass across its boundaries. Examples include boiling water in an open pot.
• Closed System: In a closed system, energy can be exchanged with the surroundings, but the transfer of matter is restricted. While heat and work can cross the boundaries, mass remains constant within the system. A sealed steam radiator is an example of a closed system.
• Isolated System: An isolated system cannot exchange either energy or matter with its surroundings. It is completely insulated from its environment. A perfect example is a thermos bottle that keeps its contents at a constant temperature for an extended period.

3.0Different Branches of Thermodynamics

Thermodynamics is classified into several branches, given below:

Classical Thermodynamics: This branch deals with the macroscopic properties of systems and uses laws and concepts without requiring knowledge of the behavior of individual particles.

Statistical Thermodynamics: This branch bridges the gap between macroscopic and microscopic worlds by explaining thermodynamic properties regarding the statistical behavior of the molecules that compose a system.

Chemical Thermodynamics: This branch examines how heat and work interact with chemical reactions or physical state changes, adhering to the principles of thermodynamics.

Equilibrium Thermodynamics: This branch studies systems in thermodynamic equilibrium, where macroscopic variables do not change over time and there are no net flows of matter or energy.

Non-Equilibrium Thermodynamics: This branch deals with systems that are not in thermodynamic equilibrium and where macroscopic variables can change over time, often involving the study of transport processes and the rate of irreversible processes.

4.0Thermodynamic Properties

• State Variables (or Thermodynamic Variables/Quantities): These properties define a system's state, which is characterized by measurable properties such as temperature, pressure, and volume. Any change in these properties indicates a change in the system's state.
• State Functions: These are state variables that depend only on the system's current state, not on the path taken to reach that state. State functions are denoted by capital letters. Examples include internal energy (E), enthalpy (H), entropy (S), Gibbs free energy (G), temperature (T), pressure (P), and volume (V).
• Path Functions: These are properties that depend on the path or mechanism followed by the system to reach its final state and the initial and final states. Path functions are denoted by lowercase letters. Examples include work done (w) and heat (q).

5.0Types of Thermodynamic Variables

• Intensive Variables: These variables are independent of the size or mass of the system. Examples include temperature, pressure, and specific heat capacity.
• Extensive Variables: These variables depend on the size or mass of the system. Examples include volume, energy, entropy, heat capacity, and enthalpy.

6.0Types of Thermodynamic Processes

Thermodynamic processes are the various ways a thermodynamic system can change its state. These processes can be defined based on how certain properties, such as pressure, volume, and temperature, are held constant or how energy is transferred within the system. Here are the main types of thermodynamic processes:

Isothermal Process

• A process that occurs at a constant temperature.
• • Heat is exchanged with the surroundings to ensure temperature remains constant.
  • The internal energy of an ideal gas does not change.
  • Example: Slow compression or expansion of a gas in a cylinder with a heat reservoir.

Adiabatic Process

• A process that occurs without any heat exchange between the system and its surroundings.
• • The system is thermally insulated.
  • Changes in internal energy result solely from work done on or by the system.
  • Example: Rapid compression or expansion of a gas in an insulated cylinder.

 Isobaric Process

• A process that occurs at a constant pressure.
• • Volume changes while pressure remains constant.
  • Heat added to or removed from the system changes the internal energy and performs work.
  • Example: Heating water at atmospheric pressure.

Isochoric  Process

• A process that occurs at a constant volume.
• • No work is done since volume does not change.
  • Any heat added to the system changes its internal energy.
  • Example: Heating a gas in a rigid, sealed container.

Cyclic Process

• A process where the system reverts to its initial state following a sequence of alterations.
• • The net change in internal energy over one cycle is zero.
  • Work done over one cycle is equal to the net heat added to the system.
  • Example: The operation of a heat engine.

 Reversible Process

•  A process that can be reversed without leaving any change in both the system and the surroundings.
• • It occurs infinitely slowly, allowing the system to always remain in equilibrium.
  • Idealization; no real process is truly reversible.
  • Example: Quasi-static processes in thermodynamic cycles.

 Irreversible Process

• A process that cannot be reversed without leaving changes in the system and surroundings.
• • Involves dissipative effects like friction, turbulence, and unrestrained expansion.
  • Real processes are typically irreversible.
  • Example: Spontaneous mixing of gases, real-world heat transfer

7.0Thermodynamic Potentials

Thermodynamic potentials measure a system's stored energy and how it transforms from its initial state to its final state. Different potentials are used depending on the system's constraints, such as temperature and pressure. Here are the main forms of thermodynamic potentials:

• Internal Energy (U): The total energy contained within the system, comprising both the capacity for performing work and the potential for releasing heat..
• Gibbs Energy (G): The energy associated with a system that can be used to do non-mechanical work. It is particularly useful in processes occurring at constant temperature and pressure.
• Enthalpy (H): The overall heat content within a system. representing the ability to do non-mechanical work and the ability to emit heat. It is especially useful for processes occurring at constant pressure.
• Helmholtz Energy (F): The energy that can be converted to both mechanical and non-mechanical work. It is particularly relevant for processes occurring at constant volume and temperature.

Enthalpy in Thermodynamics

• Enthalpy is a measure of a system's total heat content. It encompasses the system's internal energy along with the product of its pressure and volume.
• Enthalpy is a property or state function, akin to energy, and shares the same dimensions, typically measured in joules or ergs. 
• Its value solely depends on the temperature, pressure, and composition of the system, irrespective of its past states.

Entropy in Thermodynamics

• Entropy represents the amount of thermal energy per temperature unit in a system that cannot be harnessed for useful work. 
• It quantifies the molecular disorder or randomness within a system, contrasting with the ordered molecular motion that generates work.
• Entropy theory provides insights into the spontaneous direction of change for various common phenomena.

8.0The Laws of thermodynamics 

The principles of thermodynamics are foundational laws that dictate the behavior of thermodynamic systems. These laws form the foundation of classical thermodynamics and have broad applications across various fields of science and engineering.

There are indeed four laws of thermodynamics:

• Zeroth Law of Thermodynamics: This law asserts that if two systems are in thermal equilibrium with a third system, then they are also in thermal equilibrium with each other It establishes the concept of temperature and provides a basis for temperature measurement.

• First Law of Thermodynamics: Also known as the law of energy conservation, it can only change forms. It establishes the principle of energy conservation.

• Second Law of Thermodynamics: This law introduces the concept of entropy, stating that in any natural process, the total entropy of a system and its surroundings always increases (or at least remains constant in an idealized reversible process). It implies the directionality of processes and the irreversibility of natural phenomena. 

• Third Law of Thermodynamics: This law states that as the temperature of a system approaches absolute zero, the entropy of the system approaches a minimum value. It provides a baseline for the absolute entropy of substances at zero Kelvin and offers insights into the behavior of systems at low temperatures.