SECOND LAW OF THERMODYNAMICS / STATE FUNCTIONS / HEAT CAPACITY

1. Second law of thermodynamics

2. Introduction :-
• Like first law, second law is also truly a law of experience gathered
from observations of nature.
• There are no derivations from second law known.
• Anything which determines the criteria for direction of reaction forms
the base of second law.
• Mechanical work tends to transform into thermal energy.
• Eg,
hand blender, motor, automobiles etc

3. Introduction :-

4. Purpose :-
• Whether the reaction is spontaneous or not.
• It govern the direction of the process.
Second law suggests that –
all forms of energy can be converted into heat but no process is
available for converting heat so obtained, completely to other forms of
energy.

5. Statements for second law :-
• It is impossible to convert heat completely into equivalent amount of
work without producing some other change in some other part of the
system.
• All neutral and spontaneous process take place in one direction only
and are thermodynamically reversible.
• Heat cannot pass by itself from cold to hot body.
• It is impossible for a self acting machine unaided by an external source
to convey heat from cold to hot body.

6. Statements for second law :-
• Kelvin : it is impossible to use a cyclic process to transfer heat from a
reservoier and convert it into work without, at the same time
transferring it from hotter to a colder body.
• Clausius : it is impossible to construct a machine that is able to convey
heat by a cyclic process from colder to a hotter body unless the work is
done on machine by some outside agency.
• Kelvin- Plank : It is impossible to construct a heat engine which on
operating a complete cycle abstracts heat from a single body and
converts the whle of it into work without leaving changes in the
working system.

7. State functions :-
• A state function is a property of a system which has some definite
value for a particular state of the system.
• For example,
• P, V & T are state functions.

8. State functions :-
State functions have two important properties:
1). If the values of some state fuctions are fixed, the values of others are
automatically fixed.
• For eg,
For a given amount of gas if P & T are fixed, there can be only
one value of V.

9. State functions :-
State functions have two important properties:
2. Change of state depend only on initial and the final state of the
system.
For I second property, lets take an example
P
V
T
INITAL
P
V
T
FINAL

10. HEAT CAPACITY :-
• The quantity of heat required to carry out change of state depends on
how the process is carried out.

11. HEAT CAPACITY :-
• The function which relates to heat changes to temperature change
at constant volume or constant pressure with respect to
reversibility is known as heat capacity.
• Denoted by C.
• equations for constant volume and pressure.

12. HEAT CAPACITY :-
The heat capacity of a system, between any two temperature is the
quantity of heat required to raise the temperature of the system from
the lower to thr higher temperature divided by the temperature
difference.

13. HEAT CAPACITY :-