Laws of thermodynamics
The fundamental laws of thermodynamics are four, namely,
zeroth law of thermodynamics, 1st law of thermodynamics, 2nd
law of thermodynamics and 3rd law of thermodynamics.
The zeroth law of
thermodynamics state that
If
two bodies are in thermal equilibrium with a third body respectively, then they
are also in thermal equilibrium with each other,
In other word it can be stated as
if body A and body B are in thermal equilibrium with body C respectively, then
the body A is also in thermal equilibrium with body B. For a body A to be in a
thermal equilibrium with another body B, there must be a thermal contact. A
body in thermal equilibrium means the two body must have same temperature. If two bodies at different temperature are in
thermal contact, heat will flow from the colder body to the hotter body until
same temperature is maintained, we call this state as thermal equilibrium. For
two bodies to be in thermal equilibrium there must be a thermal contact. A
practical example of the above law is when you try to measure the temperature
of a body using a thermometer, the body and the thermometer must have thermal
contact and a thermal equilibrium between the thermometer and the body must be
reached before accurate reading can be made.
First law of thermodynamics
In closed
system, total energy of a thermodynamic
system is constant .
In
other word it can be stated in terms of conservation of energy as energy can
neither be created nor destroyed but can be transformed from one form to
another.
The
increase in internal energy of a system is equal to the heat supplied minus work
done by it.
Mathematically Q = U + W, where q
is the quantity of heat gained, u internal energy and w is the workdone. The
total energy of any system is constant, it neither be increase nor decrease but
can only change to work. When work is done by the system internal energy
decrease and it increase when work is done on the system.
Second law of
thermodynamics
In a cyclic process enthropy will either increase
or remain the same,
In
terms of energy conservation it states that energy transformation is not
hundred percent efficient.
In
terms of refrigerator it states it is not possible for heat to flow from colder
body to a warmer body without any work to accomplish the flow.
Every day the degree of
disorderliness in the universe increase, any process taken place tends toward
disorderliness, entropy. When liquid molecules evaporate they change from
liquid state to a gaseous state which is more disordered. When organism dies,
the disorderliness increases etc
Energy transformation is not 100%
efficient, some are lost in form of heat, hence the concept of heat engine arises,
this part that is lost is what is used in doing work, for keeping your body
warm etc
Naturally heat flow from warmer to a
colder body, for it to flow the other way, work must be done to accomplish the flow,
hence the concept of refrigerator arises.
Third law of thermodynamics
The
entropy of a perfect crystal of any pure substance approaches zero as the
temperature approaches absolute zero (0k).
Temperature is the measure of the
average kinetic energy of a (molecule or atom) body, if the temperature
increase the disorderliness (entropy) will increase and when the temperature
decreases the entropy decreases. 0K, absolute zero all atom and molecules are ideally
at rest and therefore the entropy is zero; therefore as the temperature approaches
0 Kelvin the entropy also approaches 0.
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