This document discusses reversible and irreversible processes in thermodynamics. It defines a reversible process as one whose direction can be reversed by an infinitesimal change, requiring infinite time and resulting in maximum work. Reversible processes must be carried out infinitely slowly to avoid irreversible dissipation and heat flow. For a reversible process exchanging heat with the surroundings, the entropy change is defined as the heat transfer divided by temperature. Irreversible processes are actual processes carried out in finite time that involve nonequilibrium states and crude force approximations. A reversible process allows the system and environment to return to their original states, while an irreversible process does not.

1. .

2. Reversible
process.

3. • The branch of physical science that
deals with the relations between heat and
other forms of energy (such as mechanical,
electrical, or chemical energy), and, by
extension, of the relationships between all
forms of energy.

4.  Second law of thermodynamics gives more
information about thermodynamics
processes
 Second law may be defined as
“Heat can not flow itself from colder body to
hotter body”
 The second law is also used to determine the
theoretical limits for the performance of
mostly used Engineering systems like heat
engine and heat pump.
Second Law of Thermodynamics.

5. Reversible process
• It is defined as the one whose
direction can be revered By an
infinitesimal small change in
some property of the system.
• It takes infinite time for
completion
• Work obtained in these process
is maximum.

6. • Reversible processes require
the absence of friction or
other hysteresis effects. They
must also be carried out
infinitesimally slowly.
• Otherwise pressure waves and
finite temperature gradients
will be set up in the system,
and irreversible dissipation
and heat flow will occur.
ΔSsurr=−qrevT.

7. • ΔU=q+w Changes in entropy (ΔS),
Together with changes in enthalpy (ΔH)
w=PextΔV ΔU=Qrev+Wrev.
• For a process that reversibly exchanges a
quantity of heat qrevqrev with the
surroundings, the entropy change is
defined as ΔS=qrev/T.

8. Irreversible process.
• Irreversible processes are
actual processes carried out
in finite time with real
substances.
• In irreversible processes,
mass transfer occurs
through a finite chemical
potential difference.
• No equilibrium in the
system.

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10. • work done is W=P(external)x change
in volume.
• For an irreversible expansion process,
a crude approximation to the force
exerted by the gas on the piston
(where the work is done) can be
provided by the equation
FA=Pext=nRTV−kVdVdt.

11. • A reversible process is one in which both the
system and its environment can return to exactly
the states they were in by following the reverse
path. An irreversible process is one in which the
system and its environment cannot return
to exactly the states that they were in.

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