Regents Chemistry
2013-2014
Unit Test Review: Kinetics, Thermodynamics & Equilibrium
LeChâtelier’s Principle: Considering the following example of a chemical reaction that can achieve equilibrium,
complete the following table:
N2(g) + 3H2(g) 
stress
increase P
decrease P
add heat
decrease heat
increase [H2]
increase [NH3]
decrease [N2]
decrease [NH3]
2NH3(g) + 91.8 kJ
direction of equilibrium shift
right
left
left
right
right
left
left
right
[N2]
decrease
increase
increase
decrease
decrease
increase
[H2]
decrease
increase
increase
decrease
increase
increase
increase
increase
[NH3]
increase
decrease
decrease
increase
increase
decrease
temperature
increase
decrease
increase
decrease
decrease
increase
What effect would a catalyst have on the above chemical reaction? Would increase both forward and reverse
reactions equally until equilibrium is reached; once equilibrium is reached the catalyst has no effect
PE Diagrams
The diagram below shows the reaction coordinate for a reversible catalyzed and un-catalyzed reaction. The
graph shown represents an endothermic or exothermic reaction? exothermic reaction
Referring to the diagram label what each arrow represents.
A. PE of the reactants (forward rxn)
B.
activation energy (Ea),forward catalyzed
C.
PE of the activated complex, un-catalyzed
D.
activation energy (Ea),reverse, un-catalyzed
E.
activation energy (Ea),forward, un-catalyzed
F. ΔH
G. PE of the products (forward rxn)
H. difference in Ea (catalyzed vs un-catalyzed)
I.
activation energy (Ea),reverse, catalyzed
J.
PE of the activated complex, catalyzed
What are the two driving forces in nature? enthalpy and entropy
Enthalpy: Heat energy H
-
nature prefers low energy (least amount of energy – think couch potato)
Entropy: randomness, disorder, chaos
-
S
nature prefers high entropy
Nature will favor reactions that:
1. go from high E to low E (exothermic reaction)
2. go from low entropy to high entropy
}
will be spontaneous
chemical reactions are always spontaneous when energy ↓ and chaos ↑

ΔH is
- and ΔS is +
chemical reactions are never spontaneous when energy ↑ and chaos ↓

ΔH is
+ and ΔS is -
chemical reactions are sometimes spontaneous when temperature is high and

ΔH is
- and ΔS is -
energy ↓ and chaos ↓

ΔH is
+ and ΔS is +
energy ↑ and chaos
↑
Do the following changes involve an increase or a decrease in entropy?
1.
evaporating water : H2O(l) ↔ H2O(g)
2. freezing water:
H2O(l) ↔ H2O(s)
increase in entropy
decrease in entropy
3. dissolving salt in water: NaCl(s) ↔ H2O(aq)
increase in entropy
answer key for multiple choice Q:
Q#
answer
Q#
answer
Q#
answer
Q#
answer
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
B
D
C
C
C
A
D
C
C
B
B
B
C
B
D
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
D
D
B
B
B
A
A
B
B
C
C
B
B
B
D
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
D
A
D
B
A
A
B
C
B
C
C
D
B
C
B
46
47
48
49
50
51
52
53
54
55
56
57
58
B
D
C
B
C
C
A
B
A
A
B
A
B