# Chapter 17 Outline

## 17.2 Spontaneous and Nonspontaneous Processes

This section introduces the basic idea of entropy (S) and the entropy change (S) for a reaction. The basic idea is that [delta] S relates to the "randomness or disorder" of a system. It is favorable for the entropy of a system to increase. If a reaction causes the entropy of a system to increase, this will make the reaction more favorable. The degree of randomness depends upon the temperature. As the temperature increases, the randomness increases.

## 17.6 Entropy Changes in Chemical Reactions: Calculating dSorxn

The entropy change for a reaction is calculated in several different ways.
1. One is from the standard entropy (S), found in a table. The calculations are very similar to calculating [delta] H for a reaction, using [delta] H of formation. Remember:
1. Products - Reactants
2. Include the moles of each species from the balanced equation
3. The tabulated values for S are absolute entropy.
4. S=0, for a perfect crystal at 0 K.
2. IF a system is at equilibrium (boiling point and freezing point are good examples), [delta]S can also be calculated from [delta]H for the reaction. You can think of these two factors as being in balance when a "system" is at equilibrium. then [delta]H = T [delta]S.

## 17.7 Free Energy Changes in Chemical Reactions: Calculating dGorxn

The next major concept in the chapter is Gibbs free energy ([delta]G). This is a measure of how "favorable" a reaction is. It takes both [delta] H and [delta] S into account.
1. [delta] G = [delta] H - T [delta]S. THIS EQUATION IS IMPORTANT. KNOW IT!!!
2. If the free energy of a system decreases ([delta]G is negative), the reaction is favorable, or spontaneous.
3. If the free energy of a system increases ([delta]G is positive), the reaction is not favorable and is not spontaneous.
4. If the free energy of a system does not change ([delta]G is 0), the system is at equilibrium.
5. [delta]Go of formation is often tabulated. It is used to calculate [delta]Go for a reaction (just like with [delta]H and [delta]S).
6. NOTE: the superscript o (as in [delta]Go, or [delta]Ho, or So. indicates the value for a standard system at a specific temperature (usually 25 C).

## 17.9 Free Energy and Equilibrium: Relating dGorxn and to the Equilibrium Constant (K)

Because [delta]G is a measure of how favorable a reaction is, it also relates to the equilibrium constant.
1. A reaction with a negative [delta]G, is very favorable, so it has a large K.
2. A reaction with a positive [delta]G is not favorable, so it has a small K.
3. A reaction with [delta]G = 0 is at equilibrium.
4. There are several different [delta]G's. It is important to distinguish between them.
1. [delta]Go (a delta G, with a superscript o), is the free energy change for a reaction, with everything in the standard states (gases at 1 bar, and solutions at 1 M concentration), and at a specific temperature (usually 25 C)
2. [delta]G (just delta G). This is the free energy change for a reaction that is not at the standard state.
5. The [delta]G's are related as follows. KNOW THIS EQUATION and understand how to use it:
6. [delta]G =[delta]Go + RT ln Q

Where Q is the same Q we used for calculating equilibrium (K is the special case for Q when at equilibrium.)