1
Announcements
•
Regrades – Lab TA’s or head TA
– Random photocopying of exams
•
Remember the Learning Skills Center
Last Time
•
Reaction quotient – Q
p
and Q
c
– Mathematical Relation to K
c
and K
p
– Q < K forward
:
Q > K reverse
– Omit solids in heterogeneous systems
•
Equilibrium from initial conditions
– Molar proportions
– Equilibrium tables
Equilibrium Tables
aA
→
bB
A
B
Initial concentration
[A]
[B]
Change in conc.
–ax
+bx
Equilibrium conc.
[A] – ax
[B] + bx
•
Use the definition for K
c
and solve for x
•
Sign of x determined by Q and K
←
Example – Using “x”
K
c
= 54.6 at 700 K for the reaction of hydrogen
with iodine gas to form HI(g).
Suppose that
38.4 g of HI, 5.0 g of H
2
, and 26.8 g of I
2
are
placed together in a 2 L container at this
temperature.
What are the concentrations of
each substance at equilibrium?

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