This presentation discusses thermodynamic work and processes involving changes in pressure and volume. It begins by defining work as the energy transferred by a system to its surroundings. Work can be measured in joules or newton-meters. Pressure-volume work occurs when the volume of a system changes and is represented by the area under the pressure-volume curve. An isobaric process maintains constant pressure, while an isochoric process maintains constant volume. Pressure-volume diagrams are used to visualize these processes and calculate work done on a system based on changes in pressure and volume.

1. Presentation for
THERMODYNAMICS
By: Ayesha Anum, Marwa Batool
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2. Work done by constant
volume and pressure
using PV diagram

3. What is Work?
Definition, Explanation and Units
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4. “
“In thermodynamics, work performed by
a system is the energy transferred by the
system to its surroundings.”
W = F . d
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5. Explanation:
◉ Work is a form of energy, but it
is energy in transit.
◉ A system contains no work,
work is a process done by or on
a system.
◉ In general, work is defined for
mechanical systems as the
action of a force on an object
through a distance.
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Units:
‘Newton-meter’ (Nm) or Joule (J)
WHAT IS WORK?
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6. PΔV Work
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7. “
“Pressure-volume work occurs when the volume V of a
system changes. It is equal to the area under the
process curve plotted on the PV diagram. It is known
also as boundary work.”
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8. ◉ Occurs because the mass of
substance within the system
boundary causes a force, the
pressure times the surface
area, to act on the boundary
surface and make it move.
◉ Occurs when the volume V of
a system changes.
◉ It is used for calculating
piston displacement work in
a closed system.
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◉ The pressure & temperature
may also change.
PΔV Work
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9. ◉ The first law of
thermodynamics and the work
can then be expressed as:
◉ When system changes from
an initial to a final state, it passes
through a series of intermediate
states called paths.
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◉ The work done by the
system depends on the
initial and final states and
path.
◉ Q and W are path
dependent, whereas ΔEint is
path independent.
PΔV Work
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10. Pressure-Volume Diagram
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11. “
“A pressure–volume diagram (PV diagram) is used to
describe corresponding changes
in volume and pressure in a system.”
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12. ◉ It plots the change in pressure P with
respect to volume V for a process.
◉ In thermodynamics, a set of
processes form a cycle, so on
completion of the cycle there has
been no net change in state of the
system.
◉ The figure shows an idealized PV
diagram showing a series of
numbered states (1 through 4).
◉ Paths between each state consist of
a process which alters the pressure
or volume of the system.
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Pressure Volume Diagram
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13. ◉ Amount of energy received by the
system as work can be measured as
the net work is represented by the
area enclosed by the four lines.
◉ In the figure, the processes 1-2-3
produce a work output.
◉ Processes from 3-4-1 require a
smaller energy input to return to the
starting position.
◉ Thus, the net work is the difference
between the two.
◉ This figure is highly idealized, in so
far as all the lines are straight and the
corners are right angles.
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Pressure Volume Diagram
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14. Finding Work done using PV Diagram
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15. ◉ Consider that a gas is confined to a
cylinder in contact with a thermal
reservoir at temperature T.
◉ Piston exerts a total downward force
‘mg’ on the gas, which in equilibrium
is balanced by the upward force due
to the gas pressure.
◉ The volume of the gas is determined
from the height h of the piston above
the bottom of the cylinder.
◉ The temperature of the gas is
measured with a suitable
thermometer.
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◉ lA gas supply permits additional
gas to be added to the cylinder.
◉ If the piston moves through a
distance dx, then the volume of the
gas changes by an amount dV=A
dx.
◉ Thus, the work done on the gas is
W = - ∫ P dV --- Equation 1
◉ The integral is carried out between
the initial volume Vi and the final
volume Vf .
Work done using PV Diagram
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16. Work Done at Constant Volume:
◉ The work is zero for any process
where the volume is constant as in
segment AB and CD
W = 0 (constant V)
◉ Deduce directly from equation 1
that W = 0 if V is constant.
◉ Not sufficient that the process start
and end with the same volume.
◉ So the volume must be constant
throughout the process for the
work to vanish.
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Work Done at Constant Pressure:
◉ We can apply equation 1 because
the constant P comes out the
integral:
W = -p ∫ dV = -p( Vi - Vf ) (constant P)
◉ Note that the work done on the gas
is negative for both of these
segments as the volume increases in
both processes.
PV Diagram
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17. Isobaric Process
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18. “
“An isobaric process is a thermodynamic
process change in the state of a certain amount of
matter in which the pressure remains constant.”
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19. ◉ If heat is transferred to the system,
work is done and the internal energy
of the system also changes.
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◉ In a pressure-volume diagram, it
drives a horizontal line according to
the ideal gas law.
◉ Governed by Charles's law.
◉ According to Charles's law, for a
fixed mass of ideal gas at constant
pressure, the volume is directly
proportional to the Kelvin
temperature.
◉ Regulated by the first law of
thermodynamics
Isobaric process
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20. ◉ In this process, the increase in
energy is equal to the increase
in enthalpy minus the pressure
multiplied by the increase in
volume:
ΔE = ΔH – P.ΔV.
◉ Not to be confused with isothermal
processes, which are carried out at
constant pressure or with adiabatic
processes, which do not
exchange heat.
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Isobaric process
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Examples of Isobaric process:
◉ Expansion phase of the cylinder of
an engine.
◉ Boil water in an open container.
◉ Heating of a globe due to the
effects of solar radiation.
◉ Hot air balloons experiment
isobaric and isochoric process.

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Isobaric process
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Formulas related to isobaric processes:
◉ W 1-2 = P (V 2 - V 1)
◉ W 1-2 = n R (T 2 - T 1)
◉ Q 1-2 = m c p (T 2 - T 1)
◉ Q 1-2 = (k / (k -1)) P (V 2 - V 1)

22. Isochoric Process
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23. “
“The isochoric process is
a thermodynamic process that occurs in a
constant volume.”
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24. ◉ To carry it out in a gas or liquid, it is
sufficient to heat (cool) a substance in
a container that does not change its
volume.
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◉ In an isochoric process, the
pressure of an ideal gas is directly
proportional to its temperature.
◉ In real gases, Charles's law is not
fulfilled.
◉ The graphics are represented by
lines called isochores.
◉ For an ideal gas, they are straight
lines in all the diagrams that relate
parameters: T (temperature) V
(volume) and P (pressure).
Isochoric process
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25. ◉ An isochoric thermodynamic quasi-
static process is characterized by a
constant volume, that is, ΔV = 0.
◉ Does not perform pressure-volume
work, since said work is defined by:
W = P∆V
◉ For a reversible process, the first
law of thermodynamics gives the
change in the internal energy of the
system:
dU = dQ - dW
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◉ Replace work with a change in
volume gives:
dU = dQ - PdV
◉ Since the process is isochoric, dV =
0, the previous equation now gives:
dU = dQ
◉ Using the definition of specific
heat capacity at constant volume,
CV = dU/dT ,
dQ = nCVdT
Isochoric process
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26. ◉ Integration of both sides produces:
∆Q = n 𝑻1
𝑻2
𝑪𝒗𝒅𝑻
◉ Where Cv = specific heat capacity
at constant volume.
◉ T1 is the initial temperature.
◉ T2 is the final temperature.
◉ We conclude with:
∆Q = nCV∆T
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Ideal Gas:
◉ If an ideal gas is used in an
isochoric process and the amount
of gas remains constant, then the
increase in energy is proportional
to an increase in temperature and
pressure.
◉ For example, a gas heated in a rigid
container: the pressure and
temperature of the gas will
increase.
◉ However the volume will remain
the same.
Isochoric process
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27. Practical Application of Isochoric
Process Theory:
◉ With an ideal Otto cycle, steps 2-3
and 4-1 are isochoric processes.
◉ Work done at the engine =
difference in the work which gas
will produce on the piston during
the third cycle.
◉ Work that the piston dedicates to
the gas compression during the
second cycle.
◉ In the Stirling cycle, there are also
two isochoric measures.
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◉ For its implementation, a regenerator
has been added to the Stirling
engine.
◉ Gas that passes through the filling in
one direction emits heat from the
working fluid to the regenerator.
◉ When it moves in the other direction
returns it to the work theme.
◉ The ideal Stirling cycle achieves
reversibility and the same efficiency
values as the Carnot cycle.
Isochoric process
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28. Thank You
For watching!
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