1.

System


Any quantity of matter, which contains large number of
molecules or particles bounded by a closed surface, is termed as a
system.





2.

Surroundings


Everything outside the system that is capable of exchanging
energy with the system is known as its surroundings.





3.

Isolated
System


A system that cannot exchange matter or energy with the
surroundings is an isolated system.





4.

Open
System


A system that can exchange both matter and energy with the
surroundings is an open system.





5.

Closed
System


A system that can exchange only energy with the surroundings
is a closed system.





6.

Homogeneous
and Heterogeneous System


A system, which is completely uniform throughout, is said to
be homogeneous while a system that is not uniform throughout is said to
be a heterogeneous system.





7.

Thermal
Equilibrium


A system is said to be under thermal equilibrium if its
temperature is the same in all parts of the system and is equal to the
temperature of the surroundings.





8.

Mechanical
Equilibrium


A system is said to be under mechanical equilibrium if no
unbalanced force is acting on any part of the system.





9.

Chemical
Equilibrium


A system is said be in chemical equilibrium if its chemical
composition does not change with time.





10.

Thermodynamic
Equilibrium


A system in which its observable properties like
composition, pressure, volume and temperature do not change with time is
said to be in thermodynamic equilibrium.





11.

Thermodynamic
State


A system, which is in thermal equilibrium, can be described
completely by specifying its thermodynamic coordinates such as pressure
P, volume V and temperature T. The state described by these thermodynamic
coordinates is called the thermodynamic state of the system.
Note:
 The
thermodynamic variables are not totally independent, they are
interrelated.
 Out
of the three coordinates (P, V, T), any two are sufficient to
specify the state of the system.


12.

Equation
of State


The relation concerning pressure, volume and absolute
temperature of a substance is known as the Equation of State of that
substance.
If P, V, T denote pressure, volume and temperature of a system, then
f (P, V, T) = 0 is an equation of state.
The equation of state of a system
 Depends
upon the characteristic property of the system.
 Holds
good over certain range of temperature.
Equation of State for a perfect gas
PV = nRT
Where n: number of moles of the gas
R: universal gas constant
For n = 1, PV = RT





13.

Isothermals


Isothermal Change: When a thermodynamic system undergoes
a change in its state at constant temperature, the change is said to be
an isothermal change.
The process in which the temperature of the system remains constant is an
isothermal process.
e.g. Melting or boiling of a substance.
In an isothermal change:
 The
temperature of the system is constant.
 The
change is a slow process.
 Heat
is absorbed or released during the process.
 The
internal energy of the system remains constant.
 The
heat absorbed or released is used or got from the external work done
on/by the system.
dQ = dW
An isothermal is a curve which graphically represents the
relation between pressure and volume of a gas at constant temperature.
With the help of an isothermal or isotherm, the work done in expansion
is determined to be
W = RT log_{e}

V_{2}


V_{1}




where

V_{1}: initial volume
V_{2}: final volume

^{.}.^{.}P_{1}V_{1} = P_{2}V_{2},
W = RT log_{e}

P_{1}


P_{2}







14.

Phases


The phase of a substance is defined as the form of the
substance which is chemically homogeneous, physically distinct and
mechanically separable from other forms of the same substance.
Example: The three states of a substance  solid, liquid and gaseous  are the phases
of a substance.
Phase diagram: It is a graph representing the variation of pressure (P)
with temperature (T) of the substance.
The different phases of a substance can be represented by a phase
diagram.






Phase
diagram of water


A: Triple point of water
AB: Fusion curve
AC: Vaporisation curve
AD: Sublimation curve


The curves divide the phase diagram into three regions, each
corresponding to a definite phase of water.
AB:

Fusion curve  Curve of coexistence of solid and
liquid phases.

Ice and water
remain in equilibrium along AB.

AC:

Vaporisation curve  Curve of coexistence of solid and
vapour phases.

Water and
water vapour remain in equilibrium along AC.

AD:

Sublimation curve  Curve of coexistence of solid and
vapour phases.

Water vapour
and ice remain in equilibrium along AD.

A:

Point of intersection of the three curves

 Triple point
of water.

It represents the unique condition in which all the three phases of water
coexist in equilibrium.
In case of water, the temperature corresponding to the triple point is
taken as 273.16 K.






Significance
of triple point of water


·

Its value is fixed at 273.16 K

·

In Kelvin's absolute scale, O°K is the lower fixed point
while the triple point of water is the upper fixed point.

·

The interval between the two fixed points is divided into
273.16 equal parts and each part is considered as 1K.

·

1K is the fraction

1


273.16


of the temperature of
triple point of water.








Importance
of phase diagram


·

It enables the determination of the conditions under which
different phases are in equilibrium.

·

It is useful in determination of the phase change of a
substance.

·

It is used to determine the triple point of a substance.

·

It is useful in understanding the PT relationship for a
substance.






15.

Van
der Waals' Equation of State


 Equation
of state for one mole of an ideal gas
PV = RT
 The
ideal gas equation is based on the assumptions of the kinetic theory
of gases:
 The volume of the gas molecules is negligible compared to
the total volume of the gas
 The forces of attraction between the gas molecules are
negligible.
 These
assumptions are not true at high pressures and low temperatures. The
ideal gas equation was modified by Van der Waals.
 The
corrections introduced by Van der Waals.
 Finite volume of gas molecules.
 Pressure of the gas.
 Inward
pressure due to molecules: p
p a n^{2}, n:
number of molecules per unit volume of gas
n =

N


V


N: total number of molecules



V: volume of gas

\ p a

N^{2}


V^{2}


, p a

1


V^{2}


(N = constant)

\ p =

a


V^{2}


where a is a constant

\ Corrected pressure P + p = P +

a


V^{2}



 Corrected
volume = V  b
(b is a constant for a given gas.)
Due to finite volume of molecules, space available for free motion
of molecules is less than the actual volume V of the container.

Reduction in volume due to finite molecular size


=

4


3


p (2r)^{3} where 2r =
molecular diameter.


 \ Van der Waals'
equation of state for real gas
(P +

a


V^{2}


) (V  b) = RT

 a, b are Van der Waals' constants.






