Thermodynamic equilibrium

Definition

Thermodynamic equilibrium is the state of a system where all macroscopic properties are constant over time and no net changes occur within the system or its surroundings. In this state, the system's temperature, pressure, and volume remain uniform, and there is no driving force for change, meaning that processes such as heat transfer or chemical reactions are not taking place.

5 Must Know Facts For Your Next Test

1. In thermodynamic equilibrium, no net energy is transferred as heat, and the internal energy of the system remains constant.
2. Systems can achieve thermodynamic equilibrium through various processes such as mixing or heating until uniform conditions are reached.
3. The concept of thermodynamic equilibrium applies to both closed and open systems, though it is most commonly discussed in the context of closed systems.
4. The third law of thermodynamics states that as a system approaches absolute zero, the entropy approaches a minimum value, which corresponds to a state of thermodynamic equilibrium.
5. When systems are not in thermodynamic equilibrium, they tend to evolve toward equilibrium through spontaneous processes driven by gradients in temperature, pressure, or concentration.

Review Questions

• How does thermodynamic equilibrium relate to the concept of energy transfer within a system?
  • Thermodynamic equilibrium indicates that there is no net energy transfer within a system since all macroscopic properties are stable over time. In this state, any heat transfer that occurs is balanced by work done on or by the system. As a result, both temperature and pressure become uniform throughout the system, leading to an overall steady-state condition where energy changes are not driving the system further toward equilibrium.
• Discuss how phase transitions illustrate the principles of thermodynamic equilibrium.
  • Phase transitions such as melting or boiling highlight thermodynamic equilibrium by demonstrating how different phases coexist under specific conditions. For example, at the melting point of ice, both solid ice and liquid water can exist simultaneously. During this transition, thermal energy is absorbed or released without changing temperature until the system reaches a point of equilibrium where the amounts of each phase remain constant. This showcases how systems can achieve stability at various phases while maintaining thermodynamic principles.
• Evaluate the implications of a system moving away from thermodynamic equilibrium and how it impacts its state functions.
  • When a system moves away from thermodynamic equilibrium, it creates gradients in temperature, pressure, or concentration that drive spontaneous processes to restore balance. This shift affects state functions like internal energy and entropy; for instance, internal energy may increase or decrease as the system absorbs or releases heat. The movement towards equilibrium also leads to changes in entropy, often resulting in increased disorder as the system seeks to maximize its entropy. Understanding these dynamics is crucial for predicting how real systems behave under non-equilibrium conditions.

Related terms

Isothermal Process: A process in which the temperature of a system remains constant while heat is added or removed.

Phase Equilibrium: The condition in which multiple phases of a substance coexist at equilibrium, with no net change in the amount of each phase.

Chemical Equilibrium: The state in a chemical reaction where the rates of the forward and reverse reactions are equal, leading to constant concentrations of reactants and products.