Mechanical Engineering > Thermodynamics > Equilibrium Thermodynamics

Equilibrium Thermodynamics is a foundational subfield within the larger domain of Thermodynamics in Mechanical Engineering. This branch focuses on the study of thermodynamic systems in a state of equilibrium, where there are no net flows of matter or energy, and all macroscopic changes have ceased. At equilibrium, a system’s properties remain constant over time.

Equilibrium Thermodynamics provides critical insights into the behavior of physical systems and is essential for understanding processes such as phase transitions, chemical reactions, and the efficiency of engines and refrigerators. By examining systems at equilibrium, engineers can predict how systems will respond to various changes in their environment and design more efficient and effective mechanical systems.

The First Law of Thermodynamics, which is a statement of the conservation of energy, is central to this field. It is expressed as:

\[ \Delta U = Q - W \]

where:
- \(\Delta U\) is the change in internal energy of the system.
- \(Q\) is the heat added to the system.
- \(W\) is the work done by the system.

In equilibrium thermodynamics, attention is also paid to the Second Law of Thermodynamics, which introduces the concept of entropy (\(S\)). This law states that the total entropy of an isolated system can never decrease over time, and it reaches its maximum value at equilibrium. Mathematically, this can be expressed as:

\[ \Delta S \geq 0 \]

Furthermore, the concept of free energy, such as the Helmholtz free energy (\(F\)) and the Gibbs free energy (\(G\)), is vital in predicting the direction of processes and determining the conditions for equilibrium. For instance, the Gibbs free energy is given by:

\[ G = H - TS \]

where:
- \(H\) is the enthalpy of the system.
- \(T\) is the absolute temperature.
- \(S\) is the entropy.

Equilibrium Thermodynamics also involves the application of various thermodynamic potentials and equations of state, such as the Ideal Gas Law and van der Waals equation, to describe the properties and behaviors of different substances under equilibrium conditions.

Overall, Equilibrium Thermodynamics is a crucial subject within Mechanical Engineering that provides the necessary theoretical framework for analyzing and designing systems that rely on thermodynamic processes. Understanding and applying these principles allow engineers to create systems that are both efficient and sustainable.