Score =
/25 =
%
Chapter 14.6-14.12 Diagnostic
Name: KEY
1. Write the equilibrium constant expression (K) for the following reaction.
(2 pts)
H2SO4(aq) + 2H2O(l) ⇋ SO4-2(aq) + 2H3O+(aq)
[SO4-2][H3O+]2
[H2SO4]
2. When a piece of Mg(OH)2 is put into a beaker of water, the following
equilibrium is established:
Mg(OH)2(s) ⇋ Mg+2(aq) + 2OH-(aq)
The concentration of Mg+2 is found to be 1.36 × 10-4 M. What is the value
of K for the above equation? (6 pts)
K = [Mg+2][OH-]2 = (1.36 × 10-4)(2.72 × 10-4)2 = 1.01 × 10-11
3. The K value for the following reaction is 6.2 × 10-10.
HCN(aq) ⇋ H+(aq) + CN-(aq)
When 0.2 moles of HCN are added to 1 L of water and the reaction comes
to equilibrium, what are the concentrations of all aqueous species? (6 pts)
I 0.2
C –x
E 0.2 - x
0
+x
x
6.2 × 10-10 =
0
+x
x
x2
0.2 – x
x = 1.11 × 10-5 M
0.2 – x = 0.2
4. The K value for the following equation is 240.
Pb+2(aq) + 3Cl-(aq) ⇋ PbCl3-(aq)
A solution contains the following concentrations of ions:
Pb+2: 0.2 M
Cl-: 0.1 M
PbCl3-: 0.05 M
Which way will the reaction go to reach equilibrium? Show your work.
(6 pts)
Q=
0.05
= 250
(0.2)(0.1)3
Q > K, so reaction will go left.
5. The following reaction is exothermic.
A(aq) + B(s) ⇋ C(aq) + D(g)
Predict which way the reaction will shift when the following things occur:
(5 pts)
a. Some A is removed from solution. left
b. Some B is added to the solution. no change
c. Some C is removed from the solution. right
d. The reaction vessel is cooled down. right
e. The volume of the vessel is decreased. left