CHEM1405 Worksheet 5 – Answers to Critical Thinking Questions
The worksheets are available in the tutorials and form an integral part of the learning outcomes and experience
for this unit.
Model 1: The Equilibrium Constant
1.
Kc (A) =
Kc (C) =
[!! !! ! ]
[!!! ! ]!
[!!! ! ]!
[!! !! ! ]
Kc (B) =
Kc (D) =
[!! !! ! ]!/!
[!!! ! ]
[!!! ! ]
[!! !! ! ]!/!
Kc (B) = 𝐾! (A)
2.
(a)
(b)
3.
Kc (A) = 0.078, Kc (B) = 0.280, Kc (C) = 12.8.
Kc (A) = 1 / Kc (C)
Model 2: The Reaction Quotient
1.
The reaction will shift to the right to decrease [NO2(g)].
2.
The reaction will shift to the left to increase [NO2(g)].
3.
(a)
[NO2(g)] = 2.00 M and [N2O4] = 0.20 M: Qc = 0.0500
(b)
[NO2(g)] = 1.00 M and [N2O4] = 0.20 M: Qc = 0.200.
(a)
If Qc < Kc, the reaction will shift to the right.
(b)
If Qc > Kc, the reaction will shift to the left.
4.
5.
If the first three reactions are combined by reversing each one and adding the reactions together, reaction
(4) results:
-(1)
argininosuccinate + H2O
-(2)
arginine + fumarate
-(3)
(4)
aspartate
aspartate + citrulline
argininosuccinate
fumarate + NH4
arginine + H2O
+
citrulline + NH4
Keq = 1/13
Keq = 1/4.5
Keq = 1/0.17
+
Keq = (1/13)×(1/4.5)×(1/0.17)
When a reaction is reversed, the new equilibrium constant is the reciprocal of the original value. This
has been used in the final column to obtain the equilibrium constants for the reverse of reactions (1), (2)
and (3).
When reactions are added together, the new equilibrium constant is the product of the equilibrium
constants for the individual reactions.
Overall, this gives for reaction (4):
Keq = (1/13)×(1/4.5)×(1/0.17) = 0.10
.