Thermodynamics deals with concepts of heat, temperature, and energy conversion. Thermal equilibrium occurs between substances when there is no further heat transfer between them. Internal energy is the total energy of all atoms and molecules in a substance due to their random motion. Thermodynamic systems are classified as open, closed, or isolated based on heat and matter transfer ability. The first law of thermodynamics relates heat and work through a mathematical equation. Entropy is a measure of disorder or randomness that increases for energy received by a system and decreases for energy given out. The second law of thermodynamics prohibits heat from spontaneously flowing from cold to hot without work.

1. Thermodynamics
BY SURYANSH AGRAWAL

2. Thermodynamics
Is the branch of physics that deals with the concepts of heat and
temperature and the inter-conversion of heat and other forms of energy.
Thermodynamics equilibrium
When you put a piece of ice in water at room temperature, the ice melts.
This is because the water at room temperature (higher than the ice temperature)
transfers its heat to ice and helps ice melt.
Similarly, when hot water is mixed with cold water, it
transfers its heat to the cold water.The hot water cools down. In both these
examples, we notice that the two components reach a stage where there is no
more transfer of heat.

3. Heat is something that is transferred from a substance at a higher
temperature to that at a lower temperature.
This transfer continues till the level of heat content in both the substances is
the same. Then we say that a thermal equilibrium is reached between the
two substances.
We can say that when two objects are at the same temperature, they are in
thermal equilibrium.

4. Internal energy
Internal energy is defined as the energy associated with the random,
disordered motion of the molecules of a system.
Internal energy of a system is denoted by U .
For example, a glass of water kept on a table has no kinetic energy
because it is not moving. Its potential energy can also be taken as zero.
But we know, from the kinetic theory, that the water molecules in the glass
at the given temperature move at a random speed. Thus, we can say that,
the internal energy of a substance is the total energy of all its
atoms/molecules.

5. Thermodynamic systems can be classified
on the basis of the possible transfer of heat and matter to environment.
Based on this, they are classified as open, closed or isolated systems.
● An open system is a system that freely allows exchange of energy
and matter with its environment.
● A closed system, on the other hand, does not allow the exchange of
matter but allows energy to be transferred.long as the valve is kept
closed.

6. The First law of thermodynamics
The first law of thermodynamics gives the mathematical relation between heat and
work.
∆U = Q -W
Q-heat
W-work done

7. Enthalpy is a property of a thermodynamic system, and is defined as the sum of the
system's internal energy and the product of its pressure and volume.
The total enthalpy of a system cannot be measured directly because the internal energy
contains components that are unknown, not easily accessible, or are not of interest in
thermodynamics. H=U+pV
For endothermic (heat-absorbing) processes, the change AH is a positive value; for
exothermic (heat-releasing) processes it is negative.
Endothermic processes ∆ H > 0
Exothermic processes ∆H<0
The enthalpy of an ideal gas is independent of its pressure, and depends only on its
temperature, which correlates to its internal energy. Real gases at common temperatures
and pressures often closely approximate this behavior, which simplifies practical
thermodynamic design and analysis

8. Entropy
Entropy is a scientific concept, as well as a measurable physical property that is most
commonly associated with a state of disorder, randomness, or uncertainty.
In 1865, German physicist Rudolf Clausius, one of the leading - founders of the field
of thermodynamics, defined it as the quotient of an infinitesimal amount of heat to the
instantaneous temperature.
dS=dQ/T
if the system gives up energy∆E and its entropy falls by ∆S
if the system recieves energy ∆E its entropy increses by ∆S

9. Free energy
The thermodynamic free energy is a concept useful in the thermodynamics
of chemical thermal processes in engineering and science. The change in
the free energy is the maximum amount of work that a thermodynamic
system can perform in a process at constant temperature, and its sign
indicates
therefore, only relative free energy values, or changes in free energy,
are physically meaningful, The free energy is a thermodynamic state
function, like the internal energy, enthalpy, and entropy.
The Helmholtz free energy given by F=U-TS,
The Gibbs free energy is given by G=H-TS=U + PV-TS = F +PV

10. ● The basic definition of "energy" is a measure of a body's (in thermodynamics, the
system's) ability to cause change.
● For example, when a person pushes a heavy box a few meters forward, that person
exerts mechanical energy, also known as work, on the box over a distance of a few
meters forward. The mathematical definition of this form of energy is the product of
the force exerted on the object and the distance by which the box moved (WorkForce
Distance)
● Because the person changed the stationary position of the box, that person exerted
energy on that box. The work exerted can also be called "useful energy", because
energy was converted from one form into the intended purpose, ie. mechanical
utilisation. For the case of the person pushing the box, the energy in the form of
internal (or potential) energy obtained through metabolism was converted into work in
order to push the box.

11. The First law of thermodynamics does not prevent us from converting heat
entirely into work or work entirely into heat.
These limitations lead to the formulation of another law of thermodynamics
called the Second law of thermodynamics.
The Second law of thermodynamics is a general principle which puts constraints
upon the direction of heat transfer and the efficiencies that a heat engine can
achieve.

12. The Second law of thermodynamics
“It is not possible for heat to flow from
a colder body to a warmer body without any work having been
done to accomplish this flow”.
dS=dQ/T

13. Thank you
Reference
1. NCERT
2. 4 lec ppt of biophysics by Proff. Nugzar Gomidze