Understanding Thermodynamic Equilibrium in Isolated Systems

In thermodynamics, an isolated system is one that does not exchange matter or energy with its surroundings. Thermodynamic equilibrium refers to a state where the macroscopic properties such as temperature, pressure, and chemical potential do not change over time. This means there are no net flows of energy or matter within the system nor between the system and its environment.

The Relationship Between Isolated Systems and Equilibrium

Isolated Systems Can Achieve Equilibrium

Isolated systems can reach thermodynamic equilibrium if allowed to evolve over time. For example, if you have a gas in a sealed, insulated container, over time, the gas will distribute evenly, and its temperature will become uniform throughout the container. In this state, the system is said to be in thermal equilibrium.

Characteristics of Equilibrium

At equilibrium, the system's properties become uniform, and there are no gradients such as temperature or pressure that can drive further changes. The system will also have maximum entropy, which is a measure of disorder or randomness.

Dynamic vs. Static Equilibrium

Even in equilibrium, molecular motion continues, and this is called dynamic equilibrium. However, there are no net changes in the system's macroscopic properties, meaning its temperature, pressure, and other macroscopic quantities remain constant.

Conclusion

An isolated system can be in thermodynamic equilibrium when its macroscopic properties are stable and uniform. However, if the system is not in equilibrium, it can still be considered isolated if it does not interact with its surroundings. It's important to note that whether a system is isolated or not affects how it reaches equilibrium, not whether equilibrium occurs.

For instance, if a system is floating in space, it can be in equilibrium with its surroundings, which are at around 3 Kelvin. This scenario involves the redistribution of energy throughout the system, resulting in a uniform temperature and the absence of further changes.

Two isolated systems that do not interact with each other cannot be in thermal equilibrium with each other. However, they can still be in thermal equilibrium if they are isolated from their surroundings. This is because they can redistribute energy among themselves, leading to the same temperature and other macroscopic properties within each system.

Understanding the concepts of isolated systems and thermodynamic equilibrium is crucial for many applications in physics, chemistry, and engineering. Whether you are dealing with molecules in a sealed container or understanding the cosmic microwave background radiation, these principles provide a solid foundation for further study.

Best wishes in your journey of understanding thermodynamics!