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Quiz 4 will cover the following: <b>Chapter 15 (15.1-15.7) </b><b><br>
</b><br>
<b>Sections 15.1-15.6:
</b> <br>
<br>
You need to understand how to set up an expression for the
equilibrium<br>
constant, K and how to use it. Understand how to set up K for
heterogeneous<br>
equilibria (when you have pure solids and liquids involved in the
equilibrium).<br>
What substances appear in the equilibrium constant expression? Gases
and solutes<br>
in solution but not pure solids or liquids. How do you know if
something is a<br>
pure solid or liquid? If there's and (s) or (l) for the state
symbol in the<br>
balanced equation.<br>
<br>
What does the magnitude of K tell you? Does the reaction go to
completion<br>
and by how much (mostly products or "essentially only" products)?
Does the<br>
reaction "not occur to any great extent" and how little reaction
occurs<br>
(mostly reactants or "essentially only" reactants)? Are there
appreciable<br>
amounts of reactants and products at equilibrium?<br>
<br>
Remember K depends on the form of the balanced equation and you can<br>
relate the K for one form of the balanced equation to another. When
you<br>
multiply and eqn by some factor the K for the new reaction equals
the old<br>
K RAISED to that factor (you do NOT multiply the K by that factor).<br>
(e.g. K_rev = 1/K_for or K_for<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>-1</sup>,
which makes sense since to get the reverse<br>
rxn you are essentially multiplying the forward rxn by -1). <br>
<br>
Know the relationship between equilibrium constants when you add
several<br>
balanced equations to get a new balanced equation (the K's of the
eqns<br>
being added are multiplied together to get the K for the resulting
new rxn).<br>
<br>
Know how to use an equilibrium (ICE) table and use it to determine K
from <br>
equilibrium concentrations. <br>
<br>
Know how to relate Kp and Kc. <br>
<br>
Understand the reaction quotient, Q, and how you use it with K to
predict <br>
whether the reaction is at equilibrium or not and if not which
direction <br>
does it proceed to reach equilibrium. <br>
<br>
Know how to use an ICE table to calculate equilibrium conc. starting
with <br>
initial conc. and the equilibrium constant, K. <br>
<br>
On the quiz, if you need to use an ICE table, you MUST SHOW the WORK<br>
and the ICE table. When making any assumptions you should show that
your <br>
assumptions are okay (less than 5% error). If the percent error is
greater <br>
than 5%, you need to solve the problem in a more exacting way (solve
a <br>
quadratic, method of successive approximations, etc.). You <br>
must show this work. If you don't, you will not get full credit. <br>
<br>
<b>Section 15.7: Le Chatelier's Principle </b><b><br>
</b><b> </b><br>
Understand how changing conc. shifts a reaction <br>
(AWAY from ADDED, TOWARD REMOVED). Remember adding or<br>
removing (small amounts, but not all) of a pure solid or pure liquid
will<br>
not shift a reaction. Removing all of a pure solid or pure liquid
will shift the <br>
reaction (toward the removed substance - you have to have some of
the <br>
solid or liquid to be at equilibrium when they are present in the
rxn). <br>
Adding or removing a pure liquid which is also the solvent will
cause a <br>
shift due to an indirect effect (e.g. adding solvent decreases the
conc.<br>
of the solutes causing the reaction to shift toward more moles in
solution,<br>
similar to what happens for gases when the volume is inc.).<br>
Conc. changes do NOT affect the numerical value of K.<br>
<br>
Know how changing pressure (due to volume changes) effects a
reaction. <br>
Increasing pressure (by reducing the volume) shifts the reaction
toward <br>
fewer moles of gase. Decreasing pressure (by inc. the volume)
shifts <br>
the reaction toward more moles of gas. Changing volume for a gas is<br>
essentially changing the concentration of the gases. Decreasing
volume<br>
incresaes the conc. of the gases and shifts the reaction to the side<br>
with fewer moles in solution (remember, a gas mixture is a
solution).<br>
Pressure changes do NOT affect the numerical value of K. <br>
<br>
Remember, adding an inert (non-reacting) gas to a reaction involving<br>
gases will increase the total pressure but will NOT cause a shift in<br>
the reaction because the partial pressures of the gases involved in<br>
the reaction do not change.<br>
<br>
Something similar also occurs in reactions taking place in a liquid
solution<br>
environment. When the volume of solution changes the reaction will
shift<br>
if there is a change in moles of dissolved solutes. If the volume
is<br>
increased by adding solvent the reaction will shift toward more
moles<br>
of solutes. This is like decreasing pressure by inc. volume for
gases,<br>
the reaction shifts toward more moles of gas.<br>
<br>
Also, know how changing temperature shifts a reaction AND changes
the numerical<br>
value of the equilibrium constant, K (changing conc. and pressures
do not affect<br>
the numerical value of K). How does the change in the forward and
reverse rate<br>
constants (rates) cause the shift in the equilibrium and affect K
for both<br>
exothermic and endothermic reactions? Remember, temperature changes
have a<br>
bigger affect on reactions with bigger Ea.<br>
<br>
<tt><tt><tt><b>Homework coverage (you should be able to all problems
in the given ranges)</b><b>:<br>
</b></tt></tt></tt><br>
For the 10th - 14th editions the quiz covers ch 15.<br>
You should be able do to all homework problems in ch 15.<br>
<br>
<b>For the on-line homework:</b><br>
<br>
Do all ch 15 problems.<br>
<br>
Don't forget the <b>extra homework problems</b>. They can be found
on the web at <br>
the Homework link on the class web page (CH 15 - Extra ICE Table
Problems and <br>
Solutions), <br>
<br>
<a
href="http://www.chemistry.ohio-state.edu/%7Erzellmer/chem1220/homewk/ch15_extra_problems.pdf"><b>CH
15 - Extra ICE Table Problems and Solutions</b> </a><br>
<br>
While we did finish 16.1-16.2 and start 16.3 they will not be on
this quiz.<br>
However, you need to read sections 16.1-16.2 and do the
corresponding homework<br>
from the book and skim ahead before next week.<br>
<br>
Dr. Zellmer
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