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CHAPTER 14
Concept Explorations
14.17. Chemical Equilibrium I
Part 1: You run the chemical reaction C(aq) + D(aq)  2E(aq) at 25ºC. The equilibrium constant
Kc for the reaction at this temperature is 2.0.
a.
Write the equilibrium-constant expression for the reaction.
b.
Can you come up with some possible concentrations of C, D, and E that you might observe
when the reaction has reached equilibrium at 25ºC? What are these values?
c.
A student says that only a very limited number of concentrations for C, D, and E are possible
at equilibrium. Is this true? State why you think this is true or is not true.
d.
If you start with 1.0 M concentrations of both C and D and allow the reaction to come to
equilibrium, would you expect the concentration of C to have decreased to zero? If not, what
would you expect for the concentration of C? (An approximate value is fine.)
Part 2: Consider the reaction A(aq) + B(aq)  F(aq) + G(aq), whose equilibrium constant is 1.0 × 10−5
at 20ºC. For each of the situations described below, indicate whether any reaction occurs. If reaction
does occur, then indicate the direction of that reaction and describe how the concentrations of
A, B, F, and G change during this reaction.
a.
A(aq) and B(aq) are mixed together in a container.
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Chapter 14: Concept Explorations
b.
F(aq) and G(aq) are mixed together in a container.
c.
A(aq) and F(aq) are mixed together in a container.
d.
B(aq) and G(aq) are mixed together in a container.
e.
Just B(aq) is placed into a container.
f.
Just G(aq) is placed into a container.
Consider any one of these situations in which a reaction does occur. At equilibrium, does the reaction
mixture have appreciably more products than reactants? If not, how would you describe the equilibrium
composition of the reaction mixture? How did you arrive at this answer?
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Chapter 14: Concept Explorations
14.18. Chemical Equilibrium II
Magnesium hydroxide, Mg(OH)2 , is a white, partially soluble solid that is used in many antacids. The
chemical equation for the dissolving of Mg(OH)2(s) in water is
Mg(OH)2(s)  Mg2+(aq) + 2OH−(aq)
a.
Describe a simple experimental procedure that you could use to study this solubility
equilibrium. In your experiment, how would determine when the solution process has
attained equilibrium?
b.
Write the equilibrium-constant expression for this dissolving of magnesium hydroxide.
c.
Suppose equilibrium has been established in container of magnesium hydroxide in water, and
you decide to add more solid Mg(OH)2 . What would you expect to observe? What effect will
this addition of Mg(OH)2 have on the concentrations of Mg2+(aq) and OH−(aq)?
d.
Say you have prepared an equilibrium solution of Mg(OH)2 by adding pure solid Mg(OH)2 to
water. If you know the concentration of OH−(aq), can you determine the concentration of
Mg2+(aq)? If not, what information do you need that will allow you to determine the answer?
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Chapter 14: Concept Explorations
e.
You slowly add OH− from another source (say, NaOH) to an equilibrium mixture of Mg(OH)2
and water. How do you expect the concentration of the Mg2+(aq) to change? What might you
be able to observe happening to the Mg(OH)2 (s) as you add the OH−?
f.
Next you remove some, but not all, of the Mg(OH)2 (s) from the mixture. How will this affect
the concentrations of the Mg2+(aq) and OH−(aq)
g.
If someone hands you a container of Mg(OH)2 (aq) and there is no solid Mg(OH)2 present, is
this solution at equilibrium? If it is not at equilibrium, what could you add to or remove from
the container that would give an equilibrium system?
h.
Consider an individual OH−(aq) ion in an Mg(OH)2 solution at equilibrium. If you could
follow this ion over a long period of time, would you expect it always to remain as an
OH−(aq) ion, or could it change in some way?