Untitled - Kelly Walsh High School

252 CHEMISTRY FOR THE UTTERLY CONFUSED
Get Started
17-1 The Three Laws of Thermodynamics
Don’t Forget!
Our goal in this chapter is to help you learn the laws of thermodynamics, especially
the concepts of entropy and free energy. It might be helpful to review
Chapter 6 on thermochemistry and the writing of thermochemical equations.
The concept of Gibbs free energy (G) will be useful in predicting whether or not
a reaction will occur spontaneously. Just like in all the previous chapters, in
order to do well you must Practice, Practice, Practice.
The first law of thermodynamics states that the total energy of the universe is
constant. This is simply the law of conservation of energy. We can state this relationship
as:
∆E universe ∆E system ∆ E surroundings 0
You should refer back to Chapter 6 for a discussion of the terms system, surroundings,
and universe.
The second law of thermodynamics involves a term called entropy. Entropy is
a measure of the degree that energy disperses from a localized state to one that
is more widely spread out. We may also think of entropy (S) as a measure of the
disorder of a system. The second law of thermodynamics states that all
processes that occur spontaneously move in the direction of an increase in
entropy of the universe (system surroundings). For a reversible process, a
system at equilibrium, ∆S universe 0. We can state this as:
∆S universe ∆S system ∆S surroundings > 0 for a spontaneous process
According to this second law, the entropy of the universe is continually increasing.
The third law of thermodynamics states that for a pure crystalline substance
at 0 K the entropy is zero.