The second law of thermodynamics
The second law of thermodynamics deals with the concept of
entropy. The entropy predicts the direction of the spontaneous reaction whether
the reaction is reversible, irreversible, impossible, etc.
Before going deep into the concept of the second law of
thermodynamics we need to look towards the important terms which may help out
to understand the concept of thermodynamics. A brief description of these terms are as followed:
Isolated system:
A thermodynamics system that cannot transfers or exchange
matter and energy to the boundaries of the system are called an isolated system.
It could be possible in two ways:
·
If the system is enclosed, that no matter and
energy can be transferred from its boundaries.
·
The system is so distant( so far) from another
system that no energy can be transferred to another system.
Difference between spontaneous and non -spontaneous
processes?
Spontaneous process:
The process which takes place on its own ( that does not
require any outward force to initiate ) is called a spontaneous process. For
example, rusting of iron, flow to water from higher point to lower point, etc.
Non-spontaneous process:
The process which requires some initiative ( driving
force) force to start that cannot take
place on its own is called a non- spontaneously process. For example flow of
water from a lower point to a higher point, diffusion of gas from low pressure
to higher pressure, etc.
Difference between the reversible and irreversible processes?
Reversible process:
A process can be procced in both ways forward or reverse
direction. A reaction in which products can react back to form products is
called a reversible reaction.
Irreversible process:
A process that can only proceed in one direction, in which
products cannot react back to form reactants is called an irreversible process.
The concept of the second law of thermodynamics is very
important it tells us about entropy (a measure of uncertainty) whether the
reaction is spontaneous or not. This law also specifies the direction of the
reaction, energy or heat transfer, and quality of heat transfer. This law
also provides the criterion of the feasibility of reaction whether the reaction
is possible or not. A process cannot be possible until it satisfies both the
first and second laws of thermodynamics.
Definition of the second law of thermodynamics:
What is the second law of thermodynamics?
The second law of thermodynamics states as:
“ Heat
transfers occur spontaneously from higher body temperature to lower body
temperature.”
The second law also states that the spontaneous process leads to an increase
in the entropy of the system. The second law is also known as the law of
increased entropy. In some cases, if the system is in thermal equilibrium or the
system is going through a reversible process, then the entropy of its system
and its surroundings remains constant.
Example:
·
When the radiation or conduction takes place through
some path the flow of heat is from hotter to the colder body and the entropy of the
system increases.
·
If an isolated system is partitioning by some
impermeable walls held on thermal equilibrium if the wall is removed or made impermeable
then the system reaches another thermal equilibrium state and the entropy of
the system increases.
How many ways the second law of thermodynamics can be
expressed? Describe the ways of the second law of thermodynamics?
The second law of thermodynamics is expressed in many ways.
But three statements are considered to be the most classical statement.
- ·
Clausius statement
- ·
Kelvin- plank statement
There are some principles for them which where were proposed to give the statements. Knowledge of these principles is important.
Clausius principle:
Clausius's principle was
recognized by Carnot at the time when the caloric theory of heat is considered
seriously. Carnot's statements were taken from the idea of the caloric theory.
The famous statements of Clausius principle are:
·
If the temperature difference exists, the motive
force can be produced.
·
The motive power of heat is independent of the agent
employed.
The modern terms, Carnot’s
principle states as:
“ No heat engine operating
between two reservoirs can be more efficient than Carnot engine operating
between two same reservoirs. Every Carnot engine operating between pair
of reservoirs are equally efficient, regardless of working substance and
operating system.”
Clausius statement:
In 1850, Rudolf Clausius was
leading the foundation of the second law of thermodynamics. He was examining
the relationship between heat transfer and work. He formulated his final
statement, which was published in 1854. The statement is known as the Clausius
statement.
Clausius statement states;
“ Heat cannot
spontaneously flow from cold to a hot body without the external work being
performed on the system”
For example:
In a refrigerator, heat flow from
cold to hot, when forced by the external agent.
Clausius's statement concludes
that work is required to flow heat or energy from cold body to hot body.
Carnot engine:
It estimates the maximum possible efficiency that a heat engine during the conversion process of heat into work and, conversely, working between two reservoirs can possess.
Plank principle:
In 1929, Max Planck wrote an important report about the second
law of thermodynamics. The Plank statement states that
“ The internal energy of a closed system is
increased by the adiabatic system, although the volume of the system remains
constant throughout the process. “
A closely related statement is
·
Friction pressure never does positive work.
·
It is irreversible to produce heat by friction.
It is relevant for the system
which is closed ( constant volume ) and has a constant number of moles.
Borgnakke and Sonntag proposed a statement that is complementary to plank’s principle that is
The only way by which the entropy
of a system can be decreased is by the transfer of heat from the system.
The plank principle is closely related to the kelvin
statement.
Kelvin -plank statement:
Lord kelvin expressed the second
law of thermodynamics in his kelvin statement. Kelvin’s statement states that
“ It is impossible to devise a heat engine
which absorbs energy in the form of heat from a single thermal reservoir and to deliver an equivalent amount of work.”
This means it is impossible to build
a heat engine that has 100% efficiency.
For example:
·
The perpetual motion machine of the second kind
would work only by absorbing energy as heat from the body.
·
Boating requires some energy in the form of heat
to convert into work. The water bodies comprise a huge amount of heat but it
won’t work. To drive a boat an efficient engine with fuel ( an external supply)
is required. So, it is impossible to build an engine with a single reservoir to
convert heat to work.
The second law of thermodynamics in chemical
thermodynamics:
Gibbs free
energy:
In thermodynamics, the Gibbs free energy is the
thermodynamics potential that can be used to calculate the maximum reversible
work at constant temperature and pressure. It is measured in joules.
G = H - TS
This is dummy text. It is not meant to be read. Accordingly, it is difficult to figure out when to end it. But then, this is dummy text. It is not meant to be read. Period.
ConversionConversion EmoticonEmoticon