# The First Law of Thermodynamics

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22 Φεβ 2014 (πριν από 7 χρόνια και 6 μήνες)

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The First Law of Thermodynamics

One of the most fundamental manifestations in
nature is the
energy

that accompanies all changes
and transformations
.

The most common form form in which this energy
appears, and the form to which all other tend, is
heat
.

A
study of this interrelation of the various forms of
energy in a system constitutes the subject of
thermodynamics
.

Within any system the energy may be kinetic or
potential in nature, or both.

Kinetic
energy

is the energy a system possesses by
virtue of its motion, be it molecular or motion of
the
body as a whole
.

Potential energy

is
the energy a system possesses by
virtue of it’s position. i.e., energy due to structure of
the body or due to its configuration with respect to
other bodies.

The
absolute value of the
total energy

contained in a
system: Einstein
relation E = mc
2
,

The
energies involved are so large

that any changes
in them as a result of the usual chemical or physical
processes would be negligible compared with the
totals. Further
, the changes in the masses resulting
from the energy transfers would be so small as to
beyond detection by our available means of
wheighing.

Thermodynamics
prefers to deal with
energy
differences which accompany changes in systems

since these can be measured
.

The
energies involved are so large

that any changes
in them as a result of the usual chemical or physical
processes would be negligible compared with the
totals. Further
, the changes in the masses resulting
from the energy transfers would be so small as to
beyond detection by our available means of
wheighing.

Thermodynamics
prefers to deal with
energy
differences which accompany changes in systems

since these can be measured
.

A
system

is defined as any portion of the universe
isolated in an inert container, which may be real or
imaginary, for purpouses of study of the effect of
various variables upon the contents of the system.

The
portion of the universe excluded from the
system is called its
surroundings
.

Open system

can exchange both matter and energy
with its surroundings.

Isolated system

<> Open system.

Closed system

is one in which no transfer of matter
to or from surroundings is possible, but that of
energy is.

A
phase

a homogeneous

physically distinct

mechanically separable

portion of a
system

each phase can be separated from every other
phase by such operations as a filtration,
sedimentation, decantation, or any other
mechanical means of separator

It does not include, however, such separation
methods as evaporation, distillation, adsorption or
extraction.

each phase may be
continuous

or
it may be
broken up into
smaller
portion

The phases present in a system may consist of
pure
substances

or
they may be
solutions
.

A
true solution

is defined as a physically
homogeneous mixture of two or more
substances.

This
definition of a solution places no
restriction on either the
states of
aggregation

or
relative amounts of the constituents
.

H
omogeneous

system contains only one
phase.

Heterogeneous

system more than a single phase may
be
present,
each phase is separated from every other
by a phase boundary
.

The
properties of a
system

extensive

property of a system is any properly
whose magnitude depends on the amount of
substance present.

Examples: total
mass,
volume and energy.

intensive

properties are those whose value is
independent of the total amount, but depends
of the substance
or substance in a
system. Example: pressure
,
density, refractive index, and mass, volume
, or
energy per mole.

The
principle of
reproducibility of
states
: the
states
of a system can be reproduced by
reproducing
the
values of the
variables

Partial
Molal

Quantities

𝐹
=

𝑃
,
𝑇
,

1
,

2
,


𝑗

𝐹
=
𝜕𝐹
𝜕𝑇
𝑃
,
𝑛
𝑖
𝑇

+

𝜕𝐹
𝜕𝑃
𝑇
,
𝑛
𝑖
𝑃

+
𝜕𝐹
𝜕

1
𝑃
.
𝑇
,
𝑛
𝑖


1
+

𝜕𝐹
𝜕

2
𝑃
,
𝑇
,
𝑛
𝑖


2

+

𝜕𝐹
𝜕

𝑗
𝑃
,
𝑇
,
𝑛
𝑖


𝑗

𝐹
1

=
𝜕𝐹
𝜕
1
𝑃
,
𝑇
,
𝑛
𝑖

𝐹
2
=
𝜕𝐹
𝜕
2
𝑃
,
𝑇
,
𝑛
𝑖

𝐹
𝑗
=
𝜕𝐹
𝜕
𝑗
𝑃
,
𝑇
,
𝑛
𝑖

𝐹
=
𝜕𝐹
𝜕𝑇
𝑃
,
𝑛
𝑖
𝑇

+

𝜕𝐹
𝜕𝑃
𝑇
,
𝑛
𝑖
𝑃

+
𝐹
1



1

+
𝐹
2



2

+

𝐹
𝑗



𝑗

at constant temperature and
pressure:

𝐹
=

𝐹
1



1

+
𝐹
2



2

+

𝐹
𝑗



𝑗

𝐹
=

𝐹
1


1

+
𝐹
2


2

+

𝐹
𝑗

𝑗

Euler’s theorem for homogeneous functions

𝐹
=
𝐹
1


1
+

1


𝐹
1

+
𝐹
2


2

+


2


𝐹
1

+

𝐹
𝑗


𝑗
+

𝑗


𝐹
𝑗

=
𝐹
1


1

+
𝐹
2


2

+

𝐹
𝑗


𝑗
+

(

1


𝐹
1

+

2


𝐹
1

+


𝑗

𝐹
𝑗

)

Where :
(

1


𝐹
1

+

2


𝐹
1

+


𝑗

𝐹
𝑗

)

= 0

Gibss
-
Duhem

equation: the
partial
molal

quantities
are not independent of each other, and that
variation of the one partial
molal

quantity affects the
others in the manner given by the equations.


1


𝐹
1

+


2


𝐹
1

=
0


𝐹
1

=

𝑛
2
𝑛
1

𝐹
2

slopes will be the values of
𝑉
2
at the selected
concentrations.

𝑉
=
𝑉
1


1
+
𝑉
2

2

𝑣
=
𝑉

1
+

2

𝑉
=

+

+

2

𝑉
2
=

𝜕𝑉
𝜕
=

+
2



+

+

2
=

𝑉
1


1
+

𝑉
2

=
𝑉
1


1
+


+
2

𝑉
1

=



2

1