2. LIST OF TOPICS COVERED IN PART
TWO OF THERMODYNAMICS
More Varieties of Systems
Types of thermodynamic equilibrium
Thermodynamic processes
3. VARIETIES OF SYSTEMS
A system whose state depends on the thermodynamic quantities,
is called a thermodynamic system. Apart from closed, open
and isolated systems in thermodynamics two more varieties exist
which are as follows:
Homogeneous system-a system is said to be homogeneous
when it has same chemical composition throughout. For
example mixture of gases.
Heterogeneous system- a system is said to be heterogeneous
when it consists of two or more different phase which are
homogeneous in themselves and are separated from one
another by definite bounding surfaces. For example ice in
contact with water.
4. THERMODYNAMIC EQUILIBRIUM
A system is said to be in thermodynamic equilibrium if its
macroscopic properties do not change with time.
The Initial state of the system corresponds to the starting
state. The system remains in equilibrium before any type of
interaction with the surroundings.
In the final state the system attains equilibrium after
interaction with the surroundings.
The state function gives the difference in the property of the
initial state and the final state.
Interaction with the surroundings means the transfer of
energy/ matter or both.
5. TYPES OF THERMODYNAMIC
EQUILIBRIUM
Chemical equilibrium: If the chemical composition of
various phases of the system does not change with time,
the system is said to be in chemical equilibrium.
Mechanical equilibrium: If no mechanical work is done by
one part of the system on the other part of the system, the
system is said to be in mechanical equilibrium. Equality of
forces exist during equilibrium. Forces arise due to
pressure. Pressure should not change with time
Thermal equilibrium: If there is no flow of heat from one
portion of the system to another, it is said to be in thermal
equilibrium. Equality of temperature exists during
equilibrium. Inequality in temperature will induce heat flow
from one part to other.
6. TYPES OF THERMODYNAMIC
EQUILIBRIUM
Phase equilibrium: mass of each phase should
remain constant with time. (phase means –solid,
liquid and gas phase.)
To say that a system is in equilibrium all 4
conditions must compulsorily be satisfied. If
anyone of them are not satisfied then system is not
in equilibrium.
7. THERMODYNAMIC PROCESSES
There are various types of thermodynamic processes that
help implementing thermodynamic laws for various
thermodynamic applications.(1)
The Laws of Thermodynamics are important because
they control interactions of everything in the universe -
regardless of scale. These rules stretch across every form
of science known to humankind.
8. THERMODYNAMIC PROCESSES
A thermodynamic state of any system can be changed
by process.
A process is accompanied by exchange of energy and
matter between system and surroundings.
This results in change in at least one of the state
variables of the system.
Thus, process provides path or operation by which a
system changes its state.
There are certain processes in which one particular
state variable is kept constant.
9. TYPES OF THERMODYNAMIC PROCESSES
Thermodynamic processes are known by some special names
like:-
Isothermal processes
Adabatic processes
Isobaric processes
Isochoric processes
Reversible processes
Irreversible processes
Cyclic processes
10. Isothermal Processes
A process in which the temperature of the system remains
constant through out the process is known as Isothermal
process. ∆T=0 (T=temperature)
In an isothermal process, the temperature of the system
remains constant, so the gas obeys Boyle’s law i.e.
PV= constant (P=Pressure and V= Volume)
The internal energy is a state function which depends on
the temperature. Since temperature remains constant in
Isothermal process, internal energy change also remain a
constant.
11. Isothermal processes
In such a system heat is either supplied to the system or
removed from it. Thus following two types of isothermal
processes may exist.:-
In Exothermic process, the evolved heat is given out by
the system instantaneously and thus the temperature of the
system does not rise at any stage of the process.
In Endothermic process, the required amount of heat is
absorbed instantaneously by the system from the
surrounding and thus the temperature of the system does
not fall at any stage of the process.
Examples:- Condensation, melting of ice at zero degrees
centigrade, all reaction taking place in fridge, reaction in
heat pump.
12. ADIABATIC PROCESSES
Adiabatic process occurs without transfer of heat or matter
between a thermodynamic system and its surroundings. Energy
is transferred to its surroundings only as work.
Whatever work is done on system will drive change in state
properties. Temperature being a state property may change and
also pressure, specific volume , internal energy and other state
properties as well. The first law of thermodynamics with Q=0
shows that all the change in internal energy is in the form of work
done..
The system in which such a processes takes place are thermally
insulated from the surroundings, and work done depends upon
only on the initial and final temperatures.
13. ADIABATIC PROCESSES
Example- Such process is often carried out in closed
insulated containers such as thermos bottle.
An isothermal process is a change of a system, in
which the temperature remains constant: ΔT = 0. ... In
other words, in an isothermal process, the value ΔT = 0
and therefore ΔU = 0 (only for an ideal gas) but Q ≠ 0,
while in an adiabatic process, ΔT ≠ 0 but Q = 0.
14. ISOBARIC PROCESSES
'Iso' means the same, and 'baric' means pressure.
In Isobaric process there is no change in pressure, it remains constant
during the process. Example of such process is as follows:-Pressure is
related to the amount of force that the molecules apply to the walls of
the container.
Inside a movable piston a gas is heated, thus the molecules move
faster, which would normally increase the pressure. But at the same
time the piston expands, increasing the volume and giving the
molecules more room to move. Since the walls of the container are
now bigger, the pressure can stay the same even though the
molecules are moving faster. That makes it an isobaric process.
Since the pressure is constant, the force exerted is constant and
the work done is given as PΔV. An isobaric expansion of a gas
requires heat transfer to keep the pressure constant.
15. ISOCHORIC PROCESSES
'iso' means the same and 'choric’ means volume.
An isochoric process, also called a constant-volume process, an
isovolumetric process, or an isometric process, is a thermodynamic
process during which the volume(the amount of space the material takes
up) of the closed system undergoing such a process remains constant, ,
meaning that the work done by the system will be zero.
For the simple system of two dimensions, any heat energy transferred to
the system externally will be absorbed as internal energy.
An example would be to place a closed tin can(solid, non-expandable
container)containing only air into a fire. To a first approximation, the can will
not expand. The molecules would move faster and the pressure would
increase, but the size of the container stays the same. The only change will
be that the gas gains internal energy, as evidenced by its increase in
temperature and pressure. Mathematically, δQ = dU. We may say that the
system is dynamically insulated, by a rigid boundary, from the environment.
16. THERMODYNAMIC PROCESSES
Thermo dynamic processes may be
Quasi –static:-a process that occurs infinitely slow
and it is represented by joined line on property
diagrams.
Non Quasi-static:-a process that does not occur
infinitely slow and it is represented by dashed line
on property diagrams.
17. REVERSIBLE AND NONREVERSIBLE
PROCESSES
Reversible:-it is a process that can be reversed in direction
following the same path without leaving any effect on the
system or the surrounding
Irreversible-:it is not a reversible process.
All quasi-static processes are not reversible but all
reversible processes are quasi-static.
18. CYCLIC PROCESSES
A thermodynamic cycle consists of a linked (series of) sequence of
thermodynamic processes that involve transfer of heat and work into
and out of the system, while varying pressure, temperature, and other
state variables within the system, and that eventually returns the
system to its initial state.
Properties depend only on the thermodynamic state and thus do not
change over a cycle.
Variables such as heat and work are not zero over a cycle, but rather
depend on the process.
The net work involved is the enclosed area on the P-V diagram.
A cyclic process is the underlying principle for an engine. If the cycle
goes counterclockwise, work is done on the system every cycle. An
example of such a system is a refrigerator or air conditioner.
19. SPONTANEOUS AND NONSPONTANEOUS
PROCESSES
Processes (or reactions) may be classified as follows also:
1. Spontaneous 2. Non-spontaneous
Spontaneous processes do not require energy input to proceed, whereas non-
spontaneous processes do i.e. A spontaneous process is capable of
proceeding in a given direction without needing to be driven by an outside
source of energy.
Spontaneous changes, also called natural processes, proceed when left to
themselves, and in the absence of any attempt to drive them in reverse.
The sign convention of changes in free energy follows the general convention
for thermodynamic measurements. This means a release of free energy from
the system corresponds to a negative change in free energy, but to a positive
change for the surroundings. Examples include: a smell diffusing in a room, ice
melting in lukewarm water, salt dissolving in water, iron rusting.
20. SPONTANEOUS PROCESSES
The laws of thermodynamics govern the direction of a spontaneous
process, ensuring that if a sufficiently large number of individual
interactions (like atoms colliding) are involved, then the direction will
always be in the direction of increased entropy.
Spontaneity does not imply that the reaction proceeds with great speed.
For example, the decay of diamonds into graphite is a spontaneous
process that occurs very slowly, taking millions of years. The rate of a
reaction is independent of its spontaneity, and instead depends on the
chemical kinetics of the reaction. Every reactant in a spontaneous
process has a tendency to form the corresponding product. This
tendency is related to stability.
21. NONSPONTANEOUS PROCESSES
A nonspontaneous reaction (also called an endergonic
reaction or an unfavorable reaction) is a chemical reaction
in which the standard change in free energy is positive, and
energy is absorbed. The total amount of energy is a loss (it
takes more energy to start the reaction than what is gotten
out of it) so the total energy is a negative net result.
Endergonic reactions can also be pushed by coupling them
to another reaction, which is strongly exergonic, through a
shared intermediate.
exergonic: Describing a reaction that releases energy to its
surroundings.
endergonic: Describing a reaction that absorbs energy
from its surroundings.
