THERMODYNAMIC SYSTEMS, PARAMETERS & POTENTIALS CLASS NOTES
THERMODYNAMIC SYSTEMS,
PARAMETERS & POTENTIALS
CLASS NOTES
A thermodynamic system is a
3dimensional visible space in
the universe. It has one or more thermodynamic process (or
processes) of energy conversion
from one form to other. It is
mostly conversion of heat to
work in all power producing
devices. These devices are petrol,
diesel, steam engines, gas, steam
& water turbines. In a water
turbine, it is conversion of
potential energy into kinetic
energy. It includes conversion
of work to heat in all power
consuming devices. These are
refrigerating and air conditioning
machinery, compressors, pumps,
fans and blowers. Pumps and
blowers do not convert work
into heat. It is difficult to
understand thermodynamics
without learning the thermodynamic
potentials and thermodynamic
parameters.
SURROUNDINGS
3 dimensional visible space outside (external ) to the thermodynamic system is surroundings.
BOUNDARY
The separating border between the system and the surroundings is boundary. Boundary is the demarcation where system ends and surroundings starts.
UNIVERSE
UNIVERSE = SYSTEM + BOUNDARY + SURROUNDINGS
All these are 3dimensional spaces.
TYPES OF THERMODYNAMIC SYSTEM
Three types
(i) Open System
(ii) Closed System
(iii) Isolated System
Open System
There is mass transfer & energy transfer across the boundary. Open Systems are
(i) Engine of any vehicle
(ii) Cooling tower
(iii) Desert cooler
(iv) Water heated in an open container
(v) only one component like compressor or condenser or evaporator.
(vi) Water pump
Closed System
Only energy transfer
No mass transfer
Examples of Closed Systems
(i) A refrigerator as one unit
(ii) An air conditioner
(iii) Human body
(iv) Water heated in a closed vessel
(v) An electric motor
(vi) Mixer
(vii) Grinder
Isolated System
No energy transfer and No mass transfer
There is no isolated system in actual practice. It is just a theoretical concept to make certain studies (equations) easier.
EXTENSIVE PROPERTIES
Which depend on mass.
Examples are
(i) Total volume
(ii) Total entropy
(iii) Total enthalpy
(iv) Total Internal energy
(v) Total humidity
INTENSIVE PROPERTIES
Which do not depend on mass.
Examples: Density, temperature, pressure
THERMODYNAMIC PARAMETERS AND POTENTIALS
THERMODYNAMIC PARAMETERS
The parameters are extremely important in deep understanding of thermodynamics. It enables to apply the fundamentals in real situations & makes further improvements in a system. Followings is the list of various thermodynamic parameters.

Principle of Maximum Entropy and that of Minimum Energy are equivalent.

Laws of Thermodynamics

Datum in Thermodynamics

Thermodynamic Temperature

Thermodynamic Scale

Properties Thermodynamic

Transport Properties

Temperature Entropy Chart

Pressure Enthalpy Chart

Availability, Unavailability And Irreversibility
Thermodynamic potentialsIntroduction
Pierre Durham introduced the concept of thermodynamic potentials in 1886. Josiah Willard Gibbs called these as fundamental functions. Derive these potentials from potential energy. Potential energy is the capacity to do work. Thermodynamic potential is a scalar quantity. These are not measurable. It represents the thermodynamic state of a system. Thermodynamic potentials are useful in the thermodynamics of chemical reactions. These potentials describe the noncyclic processes. There are four thermodynamic potentials.
Chemical reactions use thermodynamic potentials. They are four thermodynamic potentials. These are internal energy, the enthalpy, the Helmholtz free energy and the Gibbs free energy. All the thermodynamic potentials are energy terms. These potentials are not measurable as temperature or pressure. Find these from the measurable variables like pressure, volume and temperature. These involve the terms +pV and –TS. Thermodynamic properties are the partial derivatives of the thermodynamic potentials.
(∂U/∂T) at (V=C )=T
(∂F/∂P) at (T=C )= P
(∂G/∂V) at (T=C )=V
Useful work done under constant temperature (T) and volume( V)=ΔF
Useful work done at constant temperature (T) and constant pressure (P) conditions=ΔG
TABLE: THERMODYNAMIC POTENTIALS AND THEIR FORMULAS
Sr.No. 
Name 
Symbol 
Formula 
1. 
Internal Energy 
U 
Q—pV 
2. 
Enthalpy 
H 
U + pV 
3. 
Helmholtz free energy 
F 
U—TS 
4. 
Gibbs Free Energy 
G 
U + pV—TS 
TABLE: THERMODYNAMIC POTENTIALS AND NATURAL VARIABLES
Sr. No. 
Thermodynamic potential 
Natural variables kept constant in the process 
1. 
U 
S, V 
2. 
H 
S,p 
3. 
G 
T,p 
4. 
F 
T, V 
TABLE: THERMODYNAMIC POTENTIALS, FUNDAMENTAL EQUATION AND EQUILIBRIUM CONDITION
Sr. No. 
Thermodynamic potential 
Fundamental equation 
Equilibrium condition 
1. 
S (U, V, N) 
Entropy fundamental equation 
Maximum 
2. 
U (S, V, N) 
Internal Energy fundamental equation 
Minimum 
3. 
H (S, P, N) 
Enthalpy fundamental equation 
Minimum 
4. 
F (T, V, N) 
Helmholtz free energy fundamental equation 
Minimum 
5. 
G (T, P, N) 
Gibbs free energy fundamental equation 
Minimum 
N = Number of particles related to molecular weight
Obtain thermodynamic potentials from thermodynamic parameters. Their estimation is indirect. It is noticeable that thermodynamic potentials have multiple independent variables. There is a important feature of all the multiple variable functions. Mixed partial derivatives are independent of the order.
^{∂2}f/∂x ∂y = ^{∂2}f/∂y ∂x are same
It is Euler’ Reciprocity Law of thermodynamics.
REFERENCES

Chemical Thermodynamics, D.J.G. Ives, University Chemistry, MacDonald Technical and Scientific, 1971

Elements of Statistical Thermodynamics (2nd Edition), L.K. Nash, AddisonWesley, 1974

Thermal Physics (2nd Edition), Kittel, Charles & Kroemer, Herbert (1980).

Encyclopedia of Physics (2nd Edition, W. H. Freeman Company. McGraw Hill,”), C.B. Parker, 1994

Thermodynamics – an Engineering Approach , Cengel, Yunus A., & Boles, Michael A, McGraw Hill, 2002

Statistical Physics (2nd Edition), F. Mandl, Manchester Physics, John Wiley & Sons, 2008

Thermodynamics, From Concepts to Applications (2nd Edition), A. Shavit, C. Gutfinger, CRC Press (Taylor and Francis Group, USA), 2009