The 2nd law of thermodynamics states that for a spontaneous process, there
is a net increase in entropy. It is important to note that we must include
the change in entropy of the system as well as the surroundings when we compute
the change in entropy
have DSuniverse < 0 are not possible. We
can determine if a process is spontaneous or not by using the 2nd law, but it is
usually impossible to compute DSsurroundings
and thus we usually use the change in the Gibbs free energy
to determine if a process is spontaneous.
- DSuniverse = DSsystem +
DSsurroundings > 0
The second law is possibly the most misunderstood scientific principle. The
two most obvious misuses are
Through thermodynamics, you can show that as the entropy of a system
increases, you can get less and less useful work out of that system. If you seal
a "perpetual motion" machine inside a box which insulates it from the rest of
the universe and only extract energy from that machine, the system inside the
box will continue to gain in entropy until no useful work can be extracted, and
then the machine stops.
- Perpetual motion machines
- The statement "Evolution is impossible since entropy can't decrease".
"Evolution is impossible" is a common argument by creationists who refuse to
believe that humans evolved from ape-like ancestors. The flaw in the statement
is obvious: entropy for a system can decrease, but only at the cost of the
universe increasing in entropy. The earth is not a closed system: it receives
large amounts of low-entropy energy from the sun and radiates it back as
high-entropy heat. We may be more highly organized (lower entropy) than slime
molds, but the universe increased in entropy as humans evolved.