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Three laws of thermodynamic.
- First law
The first law of thermodynamics defines the change in internal energy
(E) from state 1 to state 2 as equal to the difference of the heat transfer
(Q) into a system and the work (W) done by the system. You should differ
the work done on the system from the work done by
the system the sign before W depends on that.
E2 - E1 = Q - W
- Second law
The second law states that there exists a useful state variable called
entropy. The change in entropy (delta S) is equal to the heat transfer
(delta Q) divided by the temperature (T).
delta S = (delta q) / T
Second Law of Thermodynamics(heat engine): It is impossible
to extract an amount of heat QH from a hot reservoir and
use it all to do work W . Some amount of heat QC must be
exhausted to a cold reservoir. This precludes a perfect heat engine.
Second Law of Thermodynamics(refrigerator): It is not possible
for heat to flow from a colder body to a warmer body without any work
having been done to accomplish this flow. Energy will not flow spontaneously
from a low temperature object to a higher temperature object. This precludes
a perfect refrigerator
.
- Third Law
A postulate related to but independent of the second law is that it
is impossible to cool a body to absolute zero by any finite process.
Although one can approach absolute zero as closely as one desires, one
cannot actually reach this limit. The third law of thermodynamics, formulated
by Walter Nernst and also known as the Nernst heat theorem, states that
if one could reach absolute zero, all bodies would have the same entropy.
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