Name:_____________
(4 points)
Chemistry 114
Fourth Hour Exam
Remember- Show all work for partial credit. Each problem is worth 14 points. You
may do any 7 problems.
1. Consider the gas phase reaction: 2SO2 (g) + O2(g) W 2SO3(g) ÄHo = -198 kJ
If the system is at equilibrium, but the following changes occur, which way will
the equilibrium shift
Change
Shift (circle one)
SO2 removed
To Right
No Change
To Left
O2 added
To Right
No Change
To Left
SO3 removed
To Right
No Change
To Left
N2 gas added (Does not react)
To Right
No Change
To Left
Decrease container volume
To Right
No Change
To Left
Decrease Temperature
To Right
No Change
To Left
2. Complete the following table:
[H+]
[OH-]
pH
pOH
2.37x10-3 M HCl
2.37x10-3
4.22x10-12
2.63
11.37
2.81x10-4 M HClO4
2.81x10-4
3.55x10-11
3.55
10.45
5x10-6 M Ca(OH)2
1x10-9
1x10-5
9
5
1x10-8 M HCl
1.1x10-7
9.1x10-8
6.96
7.04
This area left blank for scratch paper
3. I am going to put 0.150 mole of an acid into 1 liter of water. If this acid becomes 7%
ionized...
A. What is the concentration of the acid in the un-ionized form?
7% ionized means 93% un-ionized
93% = un-ionized/total x 100%
93/100 = X/.150
.93 x .150 - un-ionized = .1395M
B. What is the concentration of the acid in the ionized form?
7% = ionized/total x 100%
7/100 = X/.150
.07 x .150 - un-ionized = .0105M
C. What is the pH of the solution?
[H+] = [A-] = ionized = .0105
pH = -log (.0105) = 1.98
D. What is the Ka of the acid?
Ka=[H+][A-]/[HA] = (.0105)(.0105)/.1395 = 7.9x10-4
4. Rate the following compounds as Strong Acids (SA), Weak Acids (WA), Neutral(N),
Weak Base (WB) OR Strong base (SB)
H2SO3
___WA_______
NH3
___WB_______
K2 O
___SB_______
H2SO4
___SA_______
CO2
___WA_______
NaNO3
____N______
CH3NH2
___WB_______
5. Define or give an equation for the following terms:
pOH
-log[OH-]
2nd Law of thermodynamics
In any spontaneous process the entropy of the universe increases
Enthalpy
H=E+PV = sum of kinetic and potential E of all particles in a system
Path function
A function that depends on the path taken between two states
Intensive property
A property of a system that does not depend on the amount of material in the system
Buffer
A solution that resists changes to pH whenever acid or base is added to the solution
6A . In the following process does the ÄS of the system:
Increase (8) Decrease (9) remain the same (NC) or cannot be determined (??)
A car is built
____9______
A car is smashed in a wreck
____8______
NaCl(s) WNa+(aq) + Cl-(aq)
_____8_____
Ice Freezing at -50 C
____9______
H2O(l)6H2O(g) at 400K
____8______
H2O(l)6H2O(g) at 300K
____8______
A mixture of oil and water separates into two phases ____9______
6B. In the following process does the ÄS of the universe:
Increase (8) Decrease (9) remain the same (NC) or cannot be determined (??)
A car is smashed in a wreck
____8______
Ice melting at -5o C
____9______
Ice Freezing at +50 C
____9______
NaCl(s) 6Na+ (aq) + Cl-(aq)
____8______
H2O(l)6H2O(g) at 400K
____8______
H2O(l)6H2O(g) at 300K
____9______
A mixture of oil and water separates into two phases ____8______
7. At what temperatures will the following process be spontaneous
A.
ÄH = +19 kJ
ÄS = -60 J/K
Never Spontaneous
B.
ÄH = +19 kJ
ÄS = +60 J/K
19000/60 = 316.7K Spontaneous at T> 316.7
C.
ÄH = -19 kJ
ÄS = -60 J/K
19000/60 = 316.7K Spontaneous at T< 316.7
D.
ÄH = -19 kJ
ÄS = +60 J/K
Always spontaneous
8. The overall reaction for the corrosion of iron by oxygen (rusting) is
4Fe(s) + 3O2(g) W 2Fe2O3(s)
Using the following data, calculate the equilibrium constant for this reaction at 25oC
Substance
Fe2O3(s)
Fe(s)
O2(g)
ÄHf o(kJ/mol)
-816
0
0
So(J/K@mol)
90
25
225
ÄH = 2(-816) - [4(0) + 3(0)] = -1632 kJ
ÄS = 2(90) - [4(25)+3(225)] = 180-(100+675) = -595 J
ÄG = ÄH -TÄS
= -1632000J - 298(-595)
=-1632000 +177310 J
=-1455000 J
ÄG= -RTln(K)
-1455000 = -8.3145(298) ln(K)
-1455000/(-8.3145 x 298) = ln(K)
587 = ln(K)
e587 = K
TI-84's will give an overflow error a this point
but some calculators will say K = 9.5x10254