1. Thermodynamics

2. Important terms to remember
• System
• Surrounding
• Work done
• Heat
• Spontaneous process
• Non-spontaneous process

3. System and Surrounding
A system is defined as the part of universe which is
under study and the rest of the universe is know as the
surroundings. System is separated from surroundings
through boundaries.

4. Heat

5. Sign convention for HEAT
• Heat is denoted as “q”.
• Heat absorbed by the system is “+ve”
• Heat transferred from the system is “-ve”.

6. Work
Pressure=
force applied/total area

7. Sign convention for work done
• Work done is denoted as w
• When work is done on the system it is “+ve”.
• When work done by the system it is “-ve”.

8. First Law of thermodynamics
• Energy can neither be created nor destroyed.

9. Internal energy
The total amount of energy associated with a fixed
amount of a substance under a given set of
conditions is referred to as the internal energy of
that substance.

10. Internal energy change
ΔE = E final state – E initial state

11. Mathematical expression
• Initial internal energy = E1
• Heat involved = q
• Work done = w
Now
E2 = E1 + q + w
E2 – E1 = q + w
ΔE = q + w
Q = ΔE +w
Q =ΔE + PΔV

12. Enthalpy
• The sum of internal energy and pressure
volume energy of a system, under a particular
set of conditions, is referred to as ENTHALPY.
• It is denoted as H.
• H = E + PV
• ΔH = ΔE + PΔV

13. Spontaneous / non-spontaneous
process
Spontaneous processes Non-spontaneous processes

14. Spontaneity and Randomness
Diffusion of gases Melting of ice
The degree of randomness is known as ENTROPY
Spreading of ink in water Evaporation of water

16. Second Law of Thermodynamics
It is impossible to construct a device which operating in a cycle, has the
sole effect of extracting heat from a reservoir and performing an
equivalent amount of work.
It is impossible for a self acting machine, working in a cyclic process and
unaided by any external agency to transfer heat from a body at lower
temperature to a body at higher temperature.

17. Second Law of Thermodynamics
Whenever a spontaneous process takes place, it is
accompanied by an increase in the total entropy of the
universe( system and surrounding)
Diffusion of gases

18. Entropy and spontaneity
• Entropy is positive : the process if
spontaneous
• Entropy change is zero: Equilibrium
• Entropy change is negative: non-spontaneous.

19. Entropy in various types of systems
• Isolated system: ΔS is positive
• Open or closed system:
ΔS = ΔS system + ΔS surrounding

20. Adiabatic change and entropy
• For irreversible change:
ΔS > q irrev/ T
• For reversible change:
q= 0
ΔS = 0
• During an adiabatic change the entropy of a
system increases if the change is irreversible
while it remains constant if the change is
reversible.

21. Entropy change of the universe in a
isothermal reversible process
• ΔS system= q/T
• ΔS surrounding= -q/T
• Total change is entropy = 0
• This means that in a reversible isothermal
process there is no change in the entropy and
the entropy of the universe remains constant.

22. Entropy change of the universe in an
irreversible process
• Entropy of universe increases in an
irreversible process.

23. Thermal death

24. Helmholtz free energy
• Or work function is represented by A and is
defined as:
A = E-TS
Where E is internal energy
T is temperature
S is entropy
• Change is Helmholtz free energy
ΔA = ΔE – T ΔS

25. Gibb’s free energy
• The maximum amount of energy available to a
system during a process for doing useful work
under constant temperature and pressure
conditions is called Gibb’s free energy.
G = H – TS
• Change in Gibb’s free energy: ΔG = ΔH – T ΔS

26. Relationship between Gibb’s free
energy and Helmholtz free energy
ΔG = ΔA + P ΔV

27. Gibb’s free energy and work done
Decrease in free energy may be regarded as
• ΔA = -w
a measure of the net work done by a system
• of constantPtemperature and pressure.
ΔG = -w + ΔV
• - ΔG = w – P ΔV

28. Gibb’s free energy and spontaneity
• When ΔG is negative : spontaneous
• When ΔG is zero: equilibrium
• When ΔG is positive: non-spontaneous

29. Standard free energy change and
equilibrium constant
• The standard free energy change is defined as
the free energy change for a process for a
specified temperature in which the reactants
in their standard state are converted to
products in their standard state.
ΔG 0 = Σ Δ f G 0 products – ΣΔ f G 0 reactants
• In terms of equilibrium constant
ΔG 0 = - RT log e K

30. Home work
• For a reaction K = 1.8 x 10-7 at 300 K. What of
the value of ΔG 0 at this temperature? R =
8314 J K-1 mol -1
• Define the term entropy. How does T delta S
determine the spontaneity of a reaction?