15 Thermodynamics definitions, important points and examples

 Thermodynamics definitions, important points and example

1. System:

•    A system refers to a specific region of space that is being studied in thermodynamics.
•    It can be a physical object, a chemical reaction, or a combination of both.
•   The boundaries of a system can be real or imaginary, depending on the context of the study.
•    Understanding the properties and behavior of a system is essential in thermodynamic analysis.

    Examples: 

A gas-filled balloon, a chemical reaction vessel, a power plant.

2. Surroundings:

•    Surroundings include everything outside of the system being studied.
•    It interacts with the system and can exchange energy or matter with it.
•     The state and properties of the surroundings may influence the behavior of the system.
•    The surroundings provide a reference point for understanding the changes occurring within the system.

    Examples: 

The atmosphere surrounding a chemical reaction, the cooling water in a heat exchanger.

3. State:

•     The state of a thermodynamic system refers to its condition defined by properties like temperature, pressure, volume, and composition.
•     The state variables represent the macroscopic characteristics of the system at a given point in time.
•    The state of a system can change through processes such as heating, cooling, and expansion.
•    Thermodynamic analysis involves studying the changes in state variables during these processes.

   Examples: 

A gas in a compressed cylinder, a liquid at a specific temperature and pressure.

4. Internal Energy:

•     Internal energy is the sum of the kinetic and potential energies of the particles within a system.
•     It represents the total energy of the system's microscopic components.
•     Internal energy is influenced by factors such as temperature, pressure, and composition.
•    Changes in internal energy occur during processes involving heat transfer and work done on or by the system.

    Examples: 

Vibrational and rotational energies of molecules, the thermal energy of a substance.

5. Work:

•    Work in thermodynamics refers to the energy transferred when a force is applied to an object and it moves a certain distance.
•    Work can be done on a system or by a system, resulting in a change in the system's energy.
•    Work can take different forms, such as expansion work, electrical work, or shaft work.
•    The calculation of work involves considering the force applied and the displacement of the system.

    Examples:

 A piston pushing against a gas, an electric motor doing mechanical work.

6. Heat:

•     Heat, on the other hand, refers to the energy transferred between objects or systems as a result of a temperature difference.
•    It flows spontaneously from a region of higher temperature to a region of lower temperature.
•     Heat transfer mechanisms include conduction, convection, and radiation.
•     Heat is represented as a positive value when it is added to a system and negative when it is lost.

    Examples:

 Heat transfer from a burner to a pot, the warmth of sunlight on the Earth's surface.

7. First Law of Thermodynamics:

•     The First Law of Thermodynamics, also known as the Law of Conservation of Energy, states that the total energy of a system and its surroundings remains constant.
•    It is important to note that while energy cannot be created or destroyed, it can be converted from one form to another.
•     The first law connects the concepts of heat transfer, work, and internal energy changes in a system.
•     It provides the basis for understanding energy balance in various thermodynamic processes.

   Examples:

 Heat released during combustion, energy conversion in a heat engine.

8. Second Law of Thermodynamics:

    The Second Law of Thermodynamics expresses that in any spontaneous process, the total entropy of a system and its surroundings always increases over time.

 Entropy, defined as the measure of disorder or randomness in a system, provides insight into the direction of natural processes. 

    It sets a direction for the flow of energy and helps identify the efficiency limits of energy conversion.

    Examples: 

Heat flow from hot to cold, diffusion of gases to equalize concentration.

9. Entropy:

•    Entropy is a measure of the disorder or randomness of a system.
•     It quantifies the number of microscopic arrangements consistent with the system's macroscopic properties.
•     The increase in entropy reflects the tendency of a system to evolve towards a more probable state.
•    Entropy is related to energy dispersal and the availability of energy for useful work.

    Examples: 

Melting of ice into water, mixing of different gases.

10. Enthalpy:

•     Enthalpy is a thermodynamic function that accounts for the internal energy of a system and the product of its pressure and volume.
•      It is often associated with heat transfer occurring at constant pressure.
•     Changes in enthalpy, represented as ΔH, provide insight into heat exchange during chemical reactions and phase changes.
•     Enthalpy is used to analyze energy changes in open systems, such as chemical reactions in a lab or industrial processes.

    Examples:

 Combustion reactions, vaporization of a liquid.

11. Heat Capacity:

•      Heat capacity refers to the amount of heat required to raise the temperature of a substance by one degree Celsius.
•      It is a material-specific property that depends on the mass and composition of the substance.
•     Heat capacity is commonly measured at constant pressure (Cp) or constant volume (Cv).
•     It quantifies the ability of a substance to store thermal energy.

     Examples: 

Specific heat capacity of water, molar heat capacity of gases.

12. Adiabatic Process:

•      An adiabatic process is a thermodynamic process in which no heat is exchanged between a system and its surroundings.
•      Energy transfer occurs only through work done on or by the system.
•      Adiabatic processes are often rapid and occur without sufficient time for heat exchange to take place.
•     They are commonly encountered in certain chemical reactions and industrial applications.

    Examples: 

Rapid compression or expansion of a gas, adiabatic flame temperature in combustion.

13. Isobaric Process:

•      An isobaric process is a thermodynamic process that occurs at constant pressure.
•      The pressure of the system remains constant while other properties, such as volume and temperature, may change.
•      Isobaric processes are commonly encountered in situations where the system is in contact with a constant-pressure environment.

   Examples:

 Heating a liquid in an open container, isobaric expansion of a gas in a piston-cylinder device.

14. Isothermal Process:

•     An isothermal process is a thermodynamic process that occurs at constant temperature.
•     The temperature of the system remains constant while other properties, such as pressure and volume, may change.
•      Isothermal processes are often achieved by maintaining the system in contact with a thermal reservoir.

    Examples: 

Expansion of an ideal gas in contact with a heat bath, phase changes at constant temperature.

15. Thermodynamic Equilibrium:

•     Thermodynamic equilibrium refers to a state in which all the properties of a system are uniform and do not change over time.
•     In equilibrium, there is no net transfer of heat or work between the system and its surroundings.
•    The system's properties, such as temperature, pressure, and composition, remain constant.
•     Equilibrium can be attained through various processes, such as heating and cooling or chemical reactions.

   Examples: 

A container of gas at a uniform pressure and temperature, a mixture of gases in which all components have reached their partial pressure equilibrium.