What is meant by phase equilibria?
Phase equilibrium is the state of thermodynamic system, in which the different phases of the substance having common boundary surfaces do not vary quantitatively.
What is the criteria for phase equilibrium of a pure substance?
The criteria for phase equilibrium, established over 100 years ago by Gibbs, are that: (1) the temperature and pressure of the phases are equal, (2) the chemical potentials of each of the components in each of the phases that it is present are equal, and (3) the global Gibbs free energy is a minimum.
What are the phases of a pure substance?
A pure substance may exist in different phases. There are three principal phases solid, liquid, and gas.
What is an example of phase equilibrium?
The simplest examples of phase equilibrium are the equilibrium of a liquid and its saturated vapor, the equilibrium of water and ice at the melting point of ice, and the separation of a mixture of water and triethylamine into two immiscible layers, or phases, that differ in density.
What are the three stages of equilibrium?
At the pressure and temperature of the triple point, all three phases (solid, liquid and gas) exist in equilibrium.
What are homogeneous equilibria?
A homogeneous equilibrium is one in which all species are present in the same phase. Common examples include gas-phase or solution reactions. A heterogeneous equilibrium is one in which species exist in more than one phase. Common examples include reactions involving solids and gases, or solids and liquids.
What is the criteria of equilibrium?
For a thermodynamic system to be in equilibrium, all intensive (temperature, pressure) and extensive thermodynamic properties (U, G, A, H, S, etc) must be constants. Hence, the total change in any of those properties (dℑ ) must be zero at equilibrium.
How many phase S does mixture has?
By definition, a pure substance or a homogeneous mixture consists of a single phase. A heterogeneous mixture consists of two or more phases.
How does equilibrium exist between the phases of a substance?
The solid lines identify the temperatures and pressures at which an equilibrium exist between phases. The point at which the lines intersect represents the triple point. At the pressure and temperature of the triple point, all three phases (solid, liquid and gas) exist in equilibrium.
How is phase equilibrium reached?
We begin with a container with a fixed volume containing some liquid, and equilibrium is achieved at the vapor pressure of the liquid at the fixed temperature given. When we adjust the volume to a larger fixed volume, the pressure adjusts to equilibrium at exactly the same vapor pressure.
Are the four phases of a pure substance in equilibrium?
If four phases of a pure substance were in equilibrium ( P = 4 ), the phase rule would give F = −1, which is meaningless, since there cannot be −1 independent variables. This explains the fact that four phases of a pure substance (such as ice I, ice III, liquid water and water vapour) are not found in equilibrium at any temperature and pressure.
What is the equilibrium curve of a pure substance?
For a pure substance, equilibrium of two phases (α and β, say) obeys the condition A differential equation of the equilibrium curve follows from (6) if the thermodynamic correlations
How do you find the phase of a pure substance?
For pure substances C = 1 so that F = 3 − P. In a single phase ( P = 1) condition of a pure component system, two variables ( F = 2 ), such as temperature and pressure, can be chosen independently to be any pair of values consistent with the phase.
What is the principle of equilibrium between phases?
The basis for the rule (Atkins and de Paula, justification 6.1) is that equilibrium between phases places a constraint on the intensive variables. More rigorously, since the phases are in thermodynamic equilibrium with each other, the chemical potentials of the phases must be equal.