What is a homogeneous equilibrium system

Heterogeneous equilibria

Phase mixtures always endeavor to change their state within the scope of diffusion, either through segregation, crystallization, or chemical compounds. Nevertheless, there are mixtures that are in equilibrium and therefore remain unchanged. Here there are conditions that establish such an equilibrium.

Equilibrium Conditions and Assumptions:

  • First, differentiate between homogeneous and heterogeneous equilibria
  • Heterogeneous equilibria have more than one phase,
  • If all parts are at rest and the potential energy is minimal, there is a mechanical equilibrium,
  • In a metastable equilibrium, the parts are at rest, but can be energetically lowered even further as a result of activation,
  • If the temperature is constant in all areas, one speaks of a thermal equilibrium,
  • A chemical equilibrium, on the other hand, exists when there are no attempts at chemical reactions,
  • If there is a mechanical, thermal and chemical equilibrium, this is described comprehensively as a thermodynamic equilibrium.

Properties of thermodynamic equilibrium:

  • Pressure p = constant
  • Volume V = constant
  • Temperature T = constant
  • Composition of the components c = constant
  • Minimum of the free enthalpy G
  • G = H - TS

    H = heat content, [ideal $ \ downarrow $]
    T = temperature
    S = entropy [ideal $ \ uparrow $]

Types of equilibrium:

In the case of heterogeneous equilibrium, a distinction is made between several forms:

  • Complete miscibility in the liquid and crystalline state, as there is no melting point but a temperature range
  • Complete miscibility in the liquid state and limited miscibility in the crystalline state, common eutectic point [transition liquid $ \ rightarrow $ crystalline]
  • Complete immiscibility in the liquid and crystalline state, miscibility only given in the gaseous state,
  • Formation of connections. Components form a new phase with a melting point above or below that of the individual components.
  • Ternary systems [ternary system], here 3 phases are in equilibrium with each other.
Spatial representation of a three-component system (schematic)
  • Multi-substance systems. This system is limited to six two-component systems and four three-component systems.