entropy & free energy (ch_18) but not 18.6 or, why do chemical reactions occur?

Entropy & free energy (Ch_18) but not 18.6

Or, why do chemical reactions occur?

Definitions: Chemical

• A substance that:

• 1) An organic chemist turns into a foul odor;

• 2) an analytical chemist turns into a procedure;

• 3) a physical chemist turns into a straight line;

• 4) a biochemist turns into a helix;

• 5) a chemical engineer turns into a profit.

Review

• In chapter 6 we discussed the convertibility of energy from 1 form to another (the 1st law). Now let’s look at the 2nd law:

The 2nd Law

• The entropy of the universe increases in a spontaneous process and remains unchanged in an equilibrium process

• For a spontaneous process • For an equilibrium process

0univ sys surrS S S 0uni sys surrS S S

This stuff is related

• We learned about enthalpy is a useful measure of internal energy plus pressure volume

• Now we see that entropy is a measure of disorder

• Now we tie it all together with Gibbs free energy- the energy available to do work

Gibbs Free Energy

• G=H-TS• This is another state function• At constant temperature

G H T S

Exam Questions

• Understand order in gasses, liquids and solids and be able to arrange various compounds in increasing entropy order

• Calculate ΔS given S for reacting and product species

• Calculate ΔG and be able to predict if a reaction will occur, if heat must be added, what temperature must be reached

More Exam Questions

• Be able to predict whether entropy is increasing in a series of different reactions

• Calculate entropy of a specific reaction given values of S0 for each reactant

• Calculate

Philosophy• There is a strange property relating to entropy. There is a strange property relating to entropy.

• If we observe a very probable configuration in the past, we continue to observe a very probable If we observe a very probable configuration in the past, we continue to observe a very probable configuration! configuration!

• But if we arrange the system in a very improbable configuration in the past, it rapidly adjusts itself to But if we arrange the system in a very improbable configuration in the past, it rapidly adjusts itself to a probable one. a probable one.

• Think of a glass of water with one drop of ink in it carefully placed so it just floats there, and Think of a glass of water with one drop of ink in it carefully placed so it just floats there, and another glass with the same amount of ink thoroughly mixed.another glass with the same amount of ink thoroughly mixed.

• Let the glass with the visible drop sit for a day.Let the glass with the visible drop sit for a day.

• Look at both glasses, measure them with everything you’ve got, you cannot tell the difference.Look at both glasses, measure them with everything you’ve got, you cannot tell the difference.

• Reverse time for a day. In one glass the drop reappears, in the other, absolutely nothing Reverse time for a day. In one glass the drop reappears, in the other, absolutely nothing happens!happens!

• Entropy gives us the real arrow of time like nothing else.Entropy gives us the real arrow of time like nothing else.

• Whoa!Whoa!

•“The question of the physical foundations of the law of monotonic increase in entropy thus remains open: it may be of cosmological origin and related to the general problem of initial conditions in cosmology; the violation of symmetry under time reversal in some weak interactions between elementary particles may play some part. The answers to such questions may be achieved only in the course of further synthesis of physical theories”.

•“Statistical Physics” by L.D. Landau and E.M.Lifshitz

Or maybe it’s just a rounding error and we are a big computer model on a machine run by someone a lot smarter then we.

Albert Migliori, after a statistical check of the Poisson ratio of the corks in many wine bottles.