A system is said to be in thermodynamic equilibrium if the system is in:
thermal, chemical and mechanical equilibrium
Understanding Thermodynamic Equilibrium
A system is said to be in thermodynamic equilibrium when there are no unbalanced potentials or driving forces within the system that would cause a change of state. For a system to be in complete thermodynamic equilibrium, it must satisfy specific conditions simultaneously. These conditions relate to thermal, mechanical, and chemical states within the system and with its surroundings.
Components of Thermodynamic Equilibrium
Thermodynamic equilibrium is a multifaceted state. It requires the absence of gradients or changes that would cause macroscopic properties to vary over time. Let's look at the key components:
- Thermal Equilibrium: This means the temperature is uniform throughout the entire system. There should be no temperature differences that could drive heat transfer from one part of the system to another, or between the system and its surroundings. If there were a temperature difference, heat would flow, and the system's state would be changing, preventing it from being in thermal equilibrium.
- Mechanical Equilibrium: This implies there are no unbalanced forces within the system or between the system and its surroundings. For example, if a gas is contained in a cylinder with a piston, the pressure must be uniform throughout the gas and balanced by the force on the piston. If there's a pressure difference, work would be done, and the system's volume or pressure would change.
- Chemical Equilibrium: This condition is met when there are no chemical reactions occurring within the system, and there is no net transfer of chemical species from one phase or region to another (like diffusion or phase change). The chemical composition must be uniform or constant over time in each phase. If a chemical reaction were ongoing, the composition would be changing.
For a system to be truly in thermodynamic equilibrium, all three of these conditions – thermal, mechanical, and chemical equilibrium – must be satisfied simultaneously. The absence of any one of these means the system is not in a state of complete thermodynamic equilibrium.
Therefore, a system in thermodynamic equilibrium is in thermal, chemical, and mechanical equilibrium.
Revision Table: Types of Equilibrium
| Type of Equilibrium | Condition |
|---|---|
| Thermal Equilibrium | Uniform temperature throughout the system. No heat transfer. |
| Mechanical Equilibrium | No unbalanced forces. Uniform pressure (in the absence of gravitational effects). No net work done. |
| Chemical Equilibrium | No net chemical reactions. Uniform chemical composition in each phase. No net mass transfer between phases or regions. |
| Thermodynamic Equilibrium | Simultaneous presence of thermal, mechanical, and chemical equilibrium. |
Additional Information: Phase Equilibrium
Sometimes, phase equilibrium is also mentioned. Phase equilibrium is the state where the mass of each phase (solid, liquid, gas) remains constant. This is often considered part of chemical equilibrium, as it involves the balance of chemical potentials of the species in different phases. For example, in a system with liquid water and water vapor, phase equilibrium exists when the rate of evaporation equals the rate of condensation, leading to a constant amount of liquid and vapor at a given temperature and pressure.
Understanding thermodynamic equilibrium is fundamental in the study of thermodynamics as it defines the state towards which isolated systems evolve and is crucial for defining state properties.
Important Questions from First Law of Thermodynamics
Isothermal expansivity of an ideal gas is
The first law of thermodynamics is equivalent to the principle of conservation of
For an adiabatic process the first law of thermodynamics becomes
Heat transfer in a cyclic process are +20 kJ, -5 kJ, -10 kJ and +15kJ. Net work done for this cycle will be given by:
__________ is NOT a property of a system.
