It is defined as when there is no change in thermodynamic
property (P,V,Tetc) of system With time.
TYPESOFEQUILIBRIUM
System and surrounding equilibrium condition is
considered in three broader terms:
Thermal equilibrium: Equality of temperature between
system and surrounding
Mechanical equilibrium: Equality of pressure between system and
surrounding
Material equilibrium: No. of moles of every substance in a
definite phase remains constant with respect to time. equilibrium attained in closed vessel.
Reversible
process:
A process which is carried out so slowly that the system and the
surroundings are always in equilibrium during the process is known as a Reversible Process (quasi-static). If
this condition does not hold good, the process is said to be Irreversible.
Irreversible process:
In a reversible process the driving force is infinitesimally larger than
the opposing force. A reversible process in very slow and takes infinite time. Where
as an irreversible process completes in finite time.
Note :
This thermodynamic reversible process is
different from the “reversible reactions”. The term “Reversible reaction” only
indicates that the reaction proceeds in both the directions. A process which
proceeds without any external help is called a spontaneous process.
PROPERTIES (PARAMETER) OF A
THERMODYNAMIC SYSTEM
(1) State of the System
(A) State function or State variable
State Functions or State Variables are the physical
quantity having a definite value at a particular (present state) state and
value is independent from the fact how the system achieved that state.
Mathematical Condition for a function
to be a state function:-
There are three conditions that must be satisfied
simultaneously for a function to be state function.
(i) If ∆φ is a state function
It means change in ∮
depends only on end states and not on the path which it followed during the process.
(ii) If ∆φ is
a state function
It implies, in
cyclic integral as the end states are same, so ∆φ value will be zero.
(iii) If ∆φ = f(x, y) is a state function,
Euler's reciprocity theorem must be satisfied.
If ∮dz=0 then, are we sure that z = 0 state
function ?
"Change in state function (z) is fixed in between two states so ∆z is
also
a state function example ∆P,∆T,∆V,∆H= state function is a wrong statement"
(B) Path function
Functions which
depend on the path means how the process is carried out to reach a state from another state depends on path e.g. work & heat.
State function : Pressure, volume, temperature, Gibbs's free energy, internal energy, entropy
Path function: Work, Heat, Loss of energy due to friction
Note : S, U, H, V, T etc are state function
but ∆S, ∆U, ∆H, ∆V, ∆T, etc.are not state function. Infact ∆ terms
are not function itself and it is very misleading and frequently asked in the
exams.
(2) Properties of the System
The state of a system is defined by a particular set of its
measurable parameters called properties, by which a system can be described for
example, Temperature (T), Pressure (P) and volume (V) defines the
thermodynamics state of the system.
Intensive property: After specifying the parameter of the
system, when system is divided in parts the parameter whose value remains
unchanged due to division is known as Intensive parameter or properties. the
value of intensive is independent of the
mass (size or quantity) of the system.
Extensive
property: the parameter whose value change on division known as extensive properties and
these are depends on the mass (size, quantity) of the system.
Extensive and Intensive properties
1:
Extensive properties are additive but intensive properties are non additive.
2: Ratio
of two extensive property gives an intensive property.
3: An
extensive property can be converted into intensive property by defining it
per mole/ per gram/ per liter
Extensive properties
|
Intensive properties
|
Volume
Number of moles
Mass
Mole
Free Energy (G)
Entropy (S)
Enthalpy (H)
Internal energy (E&U)
Heat capacity
K.E.
P.E.
Gibbs free energy (G)
Resistance
Conductance
|
Refractive index
Surface tension
Viscosity
Molar Mass
Density
Free energy per mole
Specific heat capacity
Molar heat capacity
Free energy per mole
Pressure (P)
Temperature (T)
Boiling point
freezing
point etc
Molar
enthalpy
Molar
conductivity
Equivalent
conductivity
Molarity,
Normality, Mole fraction,%w/w,%V/V
EMF of
cell
|