Thermodynamic Equilibrium: It is a combined state of Mechanical,
Thermal and Chemical equilibrium.
Mechanical Equilibrium: The system has uniform pressure,
i.e. no pressure difference between two interacting systems.
Thermal Equilibrium: The system has uniform temperature,
i.e. no temperature difference between two interacting systems.
Chemical Equilibrium: There is no change in the composition
of system, i.e. there is no tendency for a chemical reaction to occur.
Stability of Equilibrium states:
The above picture tells us about the different states of
equilibrium. These are:
Stable: Where the system has a tendency to come back to its
original position, no matter how large the displacing force is.
Neutral: It attains a new state when disturbed and remains
in equilibrium there.
Metastable: On being disturbed by a very small disturbing
force, it tends to come back to its original position i.e. acts as a stable
system. But on application of large disturbing force, it gets displaced and do
not comes back to original position.
Unstable: With a very slight displacement force gets
displaced from its actual/original position and does not come back to its original
position.
Equilibrium is more stable when it is lesser energy state,
as all systems have a tendency to achieve the lowest energy state. The
different types of Energies are:
1.
Potential - due to gravity ( = mgh)
2.
Kinetic- due to its velocity( = 0.5 *mv^2)
Mechanical Energy = Potential +
Kinetic (Macroscopic State)
3.
Internal Energy (Microscopic State)
Types of Internal Energy: Translation, Rotational,
Vibrational, Electron motion and Nucleus-nucleus interaction.
Thus, Total Energy = Kinetic + Potential + Internal
But in thermodynamics we study change of energy in a system
where the Potential and kinetic energy of the system is constant. Thus we only
consider changes in internal Energy.
Thus in thermodynamics,
Change in Energy = Change in Internal Energy.
