CHM 2046C Module10 Name:___________
Chapter 13 McMurry Homework Packet
Module Ten:
Chemical Equilibria Chapter 13 |
Possible |
Actual |
|
A.
Equilibrium Constant Derivation from Reaction Rates Lecture |
5 |
|
|
B. Writing Equilibrium
Constant Expressions |
5 |
|
|
C. Meaning
of the Equilibrium Constant: K;
|
5 |
|
|
D. Meaning
of the Equilibrium Quotient: Q;
|
5 |
|
|
E. Determination of
Equilibrium Constants from Lab Data |
10 |
|
|
10 |
|
|
|
G. Determination of
Equilibrium Conc from Kc Problems |
10 |
|
|
H. Disturbing a Chemical
Equilibrium |
5 |
|
|
5 |
|
|
|
Module Ten
Total: |
65 |
|
|
Part A: Equilibrium Constant Derivation 5 points
Derive the equilibrium constant expression
[C]c [D]d |
Kc
= --------------- |
[A]a [B]b |
from the rate expressions of the following reversible reaction:
aA
+ bB ç è cC
+ dD
Part B: Equilibrium Constant Expressions 5 points
Write equilibrium constant expressions, Kc, for the following reactions they represent:
a. PCl3 (g) + Cl2 (g) ç è PCl5 (g)
Kc =
b. 2 NOCl (g) ç è 2 NO (g) + Cl2 (g)
Kc =
c. 4 HCl (g)
+ O2 (g) ç è 2 H2O (g) +
2 Cl2 (g)
Kc =
d. CS2 (g) + H2 (g) ç è CH4 (g) + H2S (g)
Kc =
e. CaCO3 (s) ç è CaO (s) + CO2 (g)
Kc =
f. NH3
(g) + H2O (l) ç è NH4
1+(aq)
+ OH1- (aq)
Kc =
Part C:
The Equilibrium Constant K &
Expression 5 points
Write five statements which explain what the equilibrium constant expression represents:
a)
b)
c)
d)
e)
Write five useful statements about the equilibrium constant:
a)
b)
c)
d)
e)
Part D:
Equilibrium Constant, K & The
Reaction Quotient, Q 5 points
Make three generalizations concerning the composition of equilibrium
mixtures:
a)
b)
c)
Determining a reaction quotient is useful for two reasons, state the reasons:
a)
b)
Demonstrate the Usefulness of the
reaction Quotient:
The brown gas nitrogen
dioxide, NO2, will exist in equilibrium with the colorless gas, N2O4,
K = 170 at 298 K.
2 NO2 (g) ß à
N2O4 (g)
K = 170
Suppose that, at a
specific time, the concentration of NO2 is 0.015M, the concentration
of N2O4 is 0.025M.
a) Is
the Quotient Q larger than, or smaller than, or equal to K?
b) If
the system is not a equilibrium, in which direction
will the reaction proceed to achieve equilibrium?
Picture
Interpretation:
The Reaction A2 + B2 <====>
2 AB has an equilibrium constant Kc = 4. The following pictures represent
reaction mixtures that contain A2 molecules (red), B2
molecules (blue) and AB molecules:
a) Which reaction
mixtures is at equilibrium?
b) For the reaction
mixtures that are not at equilibrium, will the net reaction go in the forward
or the reverse direction to react equilibrium?
Part E: Experimental Determination of Equilibrium Constants 5 points
Calculate the equilibrium constant at 25oC for the reaction:
2 NOCl(g) ç è 2 NO (g) +
Cl2
when 2.00 moles of NOCl were placed in a 1.00-L flask, and the concentration of NO after equilibrium was achieved was 0.66 moles/liter.
|
[ ] |
[ ] |
[ ] |
Initial |
|
|
|
Change |
|
|
|
Equilibrium |
|
|
|
Part E: Experimental determination of Equilibrium Constants 5 points
A solution is prepared
by dissolving 0.050 mol of diiodocyclohexane, C6H10I2
in the solvent CCl4. The total solution is 1.00 Liter. When the
reaction:
C6H10I2
ß à C6H10 +
I2
has
come to equilibrium at 35oC. The concentration of the I2
is 0.035 M.
(a)What
are the concentrations of C6H10I2 and C6H10
at equilibrium?
|
[ ] |
[ ] |
[ ] |
Initial |
|
|
|
Change |
|
|
|
Equilibrium |
|
|
|
(b)
Calculate the K, the equilibrium constant.
Part F. Calculation Equilibrium Concentrations from Initial Concentrations based on Kc 5 points
At 25oC, Kc=0.090 for the reaction:
H2O (g) + Cl2O (g) ç è 2 HOCl (g)
Calculate the concentration of all species if 2.0 mole of pure H2O and 2.0 mole of pure Cl2O are placed in a 2.0 L flask and the system is allowed to come to equilibrium.
|
[ ] |
[ ] |
[ ] |
Initial |
|
|
|
Change |
|
|
|
Equilibrium |
|
|
|
Part F. Calculations based on Kc 5 points
The reaction
. N2 (g) +
O2 (g) ç è 2 NO
(g)
contributes to air pollution whenever fuel is burned at high temperatures and high pressure in an automobile gasoline engine. At 1500 K, K= 1.0 x 10 -5. Suppose a sample of air has
[N2] = 0.80 M and [O2] = 0.20 M before any reaction occurs. Calculate the equilibrium concentrations of the reactants and the products after the mixtures reaches 1500 K?
|
[ ] |
[ ] |
[ ] |
Initial |
|
|
|
Change |
|
|
|
Equilibrium |
|
|
|
Part G: LaChatelier’s Principle 5 points
Consider the isomerism of butane with an equilibrium constant of Kc = 2.5.
CH3
|
CH3-CH2-CH2-CH3 (n-butane) ç è CH3-CH-CH3 (isobutane)
The system is originally at equilibrium with [n-butane]=1.0 M and [isobutane]=2.5M.
(a) If 0.50 moles/liter of isobutane is suddenly added and the system shifts to a new equilibrium position, what is the equilibrium concentration of each gas?
|
[ ] |
[ ] |
Initial |
|
|
Change |
|
|
Equilibrium |
|
|
Part G: LaChatelier’s Principle 5 points
Carbonyl bromide decomposes to carbon monoxide and bromine gas.
COBr2 (g) ß à CO (g)
+ Br2 (g)
K is 0.190 at 73oC. Suppose you placed 0.500 moles of COBr2 in a 1.00-L flask and heated it to 73oC. After equilibrium had been achieved, you added an additional 3.00 mol of CO.
Calculate the equilibrium concentration of each component before the CO is added:
|
[ ] |
[ ] |
[ ] |
Initial |
|
|
|
Change |
|
|
|
Equilibrium |
|
|
|
How is the equilibrium mixture affected by adding more CO?
When equilibrium is reestablished, what are the new equilibrium concentrations of each component?
How has the addition of CO affected the concentration of COBr2 that decomposed?
Part H: LaChatelier’s
Principle Questions 5 points
Based on the followinq Equations, use the choices to describe the equibrium shifts, if any, when the following conditions are changed:
a. shifts left b. shifts right c.
No effect
4 HCL (g) +
O2 (g) ç è 2 H2O (g) + 2
CL2 (g)
_____1. 1 mole of
Chlorine gas is injected after equilibrium is reached
_____2. Water is
removed after equilibrium is reached
_____3. Additional Heat is applied to system after
equilibrium is reached,
(the
reaction is exothermic)
_____4. Nitrogen gas
is injected into the vessel after equilibrium is reached
_____5. Additional Oxygen
gas is injected after equilibrium is reached
_____6. Increasing the
size of the vessle from 1 to 3 liters after eq is reached
PCL5 çè PCl3 + CL2
_____7. Chlorine gas
is injected into the vessle
_____8. Additional Heat is added to
the system after equilibrium is achieved
(the reaction is endothermic)
_____9. Nitrogen gas
is injected into the vessle
_____10. The gases are compressed
into a vessle ½ half the original size
after
equilibrium is achieved.
Part I:
Discussion Questions 5 points
1. What is dynamic equilibrium?
2. What is true about the
initial rate of the forward and reverse reactions in a system where only
reactants are present?
b. What happens to the value of K when the
reaction is reversed?
c. What happens to the value of K when
the temperature is changed for the reaction?
4. Your textbook introduces the concept of equilibrium by noting that no reaction goes fully to
completion. What does this imply about
the reverse reaction?
5. Discuss the relationship between the magnitude of the equilibrium
constants as to whether the forward
or the reverse reaction is favored.
6. What effect does adding a catalyst
on the concentrations of the reactants and products after equilibrium is
established.
7. What disturbances
are possible for a system in equilibrium?
8. When is it reasonable to neglect the change in the concentration in the denominator of an equilibrium constant expression when solving for the equilibrium concentrations from the initial concentrations.. (When does 1.0 M – x ~ 1.0