Quiz 4 material

[robert zellmer]

Quiz 4 will cover the following: *Chapter 15 (15.1-15.7) **
*
*Sections 15.1-15.6: *

You need to understand how to set up an expression for the equilibrium
constant, K and how to use it.  Understand how to set up K for heterogeneous
equilibria (when you have pure solids and liquids involved in the 
equilibrium).
What substances appear in the equilibrium constant expression? Gases and 
solutes
in solution but not pure solids or liquids.  How do you know if 
something is a
pure solid or liquid?  If there's and (s) or (l) for the state symbol in the
balanced equation.

What does the magnitude of K tell you?  Does the reaction go to completion
and by how much (mostly products or "essentially only" products)? Does the
reaction "not occur to any great extent" and how little reaction occurs
(mostly reactants or "essentially only" reactants)?  Are there appreciable
amounts of reactants and products at equilibrium?

Remember K depends on the form of the balanced equation and you can
relate the K for one form of the balanced equation to another.  When you
multiply and eqn by some factor the K for the new reaction equals the old
K RAISED to that factor (you do NOT multiply the K by that factor).
(e.g. K_rev = 1/K_for or K_for^-1, which makes sense since to get the 
reverse
rxn you are essentially multiplying the forward rxn by -1).

Know the relationship between equilibrium constants when you add several
balanced equations to get a new balanced equation (the K's of the eqns
being added are multiplied together to get the K for the resulting new rxn).

Know how to use an equilibrium (ICE) table and use it to determine K from
equilibrium concentrations.

Know how to relate Kp and Kc.

Understand the reaction quotient, Q, and how you use it with K to predict
whether the reaction is at equilibrium or not and if not which direction
does it proceed to reach equilibrium.

Know how to use an ICE table to calculate equilibrium conc. starting with
initial conc. and the equilibrium constant, K.

On the quiz, if you need to use an ICE table, you MUST SHOW the WORK
and the ICE table.  When making any assumptions you should show that your
assumptions are okay (less than 5% error).  If the percent error is greater
than 5%, you need to solve the problem in a more exacting way (solve a
quadratic, method of successive approximations, etc.).  You
must show this work.  If you don't, you will not get full credit.

*Section 15.7:  Le Chatelier's Principle **
***
Understand how changing conc. shifts a reaction
(AWAY from ADDED, TOWARD REMOVED).  Remember adding or
removing (small amounts, but not all) of a pure solid or pure liquid will
not shift a reaction.  Removing all of a pure solid or pure liquid will 
shift the
reaction (toward the removed substance - you have to have some of the
solid or liquid to be at equilibrium when they are present in the rxn).
Adding or removing a pure liquid which is also the solvent will cause a
shift due to an indirect effect (e.g. adding solvent decreases the conc.
of the solutes causing the reaction to shift toward more moles in solution,
similar to what happens for gases when the volume is inc.).
Conc. changes do NOT affect the numerical value of K.

Know how changing pressure (due to volume changes) effects a reaction.
Increasing pressure (by reducing the volume) shifts the reaction toward
fewer moles of gase.  Decreasing pressure (by inc. the volume) shifts
the reaction toward more moles of gas. Changing volume for a gas is
essentially changing the concentration of the gases.  Decreasing volume
incresaes the conc. of the gases and shifts the reaction to the side
with fewer moles in solution (remember, a gas mixture is a solution).
Pressure changes do NOT affect the numerical value of K.

Remember, adding an inert (non-reacting) gas to a reaction involving
gases will increase the total pressure but will NOT cause a shift in
the reaction because the partial pressures of the gases involved in
the reaction do not change.

Something similar also occurs in reactions taking place in a liquid solution
environment. When the volume of solution changes the reaction will shift
if there is a change in moles of dissolved solutes.  If the volume is
increased by adding solvent the reaction will shift toward more moles
of solutes.  This is like decreasing pressure by inc. volume for gases,
the reaction shifts toward more moles of gas.

Also, know how changing temperature shifts a reaction AND changes the 
numerical
value of the equilibrium constant, K (changing conc. and pressures do 
not affect
the numerical value of K).  How does the change in the forward and 
reverse rate
constants (rates) cause the shift in the equilibrium and affect K for both
exothermic and endothermic reactions?  Remember, temperature changes have a
bigger affect on reactions with bigger Ea.

*Homework coverage (you should be able to all problems in the given 
ranges)**:
*
For the 10th - 14th editions the quiz covers ch 15.
You should be able do to all homework problems in ch 15.

*For the on-line homework:*

Do all ch 15 problems.

Don't forget the *extra homework problems*.  They can be found on the 
web at
the Homework link on the class web page (CH 15 - Extra ICE Table 
Problems and
Solutions),

*CH 15 - Extra ICE Table Problems and Solutions* 
<http://www.chemistry.ohio-state.edu/%7Erzellmer/chem1220/homewk/ch15_extra_problems.pdf>

While we did finish 16.1-16.2 and start 16.3 they will not be on this quiz.
However, you need to read sections 16.1-16.2 and do the corresponding 
homework
from the book and skim ahead before next week.

Dr. Zellmer
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