Equilibrium
Name ______________________________
Le Chatelier’s Principle
Period _____________ Date ____________
1. In a chemical reaction, a dynamic equilibrium is established when the rate of the forward reaction is
_________________ to the rate of the reverse reaction, as represented by the general equation:
A + B  C + D
2. Now we will consider factors that disturb this equilibrium, causing either:
a. the forward reaction to increase, producing a shift to the right in the equilibrium
b. the reverse reaction to increase, producing a shift to the left in the equilibrium
3. Factor #1 – Concentration
If more molecules of “A” are added to the system at equilibrium, then there will be more collisions
between “A” molecules and the remaining “B” molecules, producing more the products, “C” and
“D,” causing the equilibrium to shift to the right.
4. Suppose more molecules of “C” are added to the system: the increased number of “C” molecules
can react with _______ molecules, forming more molecules of __________.
5. In other words, when more molecules of “C” are added to the system, the equilibrium shifts to the
left, forming more (reactants / products).
6. In the following system:
2H2O  2H2 + O2
If more H2O is introduced, will there be (more / less) H2 and O2 formed?
7. Therefore, to relieve the stress of extra H2O, the equilibrium shifts to the (right / left) forming more
(products / reactants).
8. Considering the same system used in #6, if more H2 is added to the system, which reaction is
increased? (forward / reverse)
9. Therefore, to relieve the stress of extra H2, the equilibrium shifts to the (right / left).
10. Factor #2 – Pressure
Review Avagadro’s Hypothesis :
_________________________________________________________________________________
_________________________________________________________________________________
11. Given: 2 A(g) + B(g) 
C(g) + D(g)
If the above system is gaseous, in a closed container, at a constant temperature, then there are 3 volumes
of reactants to every 2 volumes of products. If the pressure is increased on the system, (according to
Boyle’s Law, increased pressure means ______________ volume), then the system will try to occupy a
smaller volume which is accomplished by forming more products because 2 volumes occupy less space
than 3 volumes. Therefore, the _____________ reaction will increase forming more C and D.
12. Conversely, if pressure is decreased, then the system will occupy a larger volume, which means the
(forward / reverse) reaction will increase, forming more (products / reactants).
13. 2H2O(g)  2H2(g) + O2(g)
In the above gaseous system, at constant temperature, if the pressure is increased, which reaction will
increase (forward / reverse)? (More / Less) products will form; (more / less) reactants will form.
14. CO(g) + NO2(g)  CO2(g) + NO(g)
Suppose the pressure on the above system is increased, which will increase (products/ reactants)?
15. Factor #3 Temperature
A + B  C + D + heat
Note that the above reaction, reading from the left to right is exothermic, i.e., it ______________ heat.
Note that, reading from the right to left, the reverse reaction is endothermic, i.e., it ____________ heat.
If the temperature is increased on the above system, then the reaction which absorbs or uses heat will be
increased, in this case, the reverse reaction ______________.
16. 2HI  H2 + I2 + heat
If the temperature is increased, there be (more / less) HI formed as the result.
17. CH2OH + heat  CO + 2H2
If the temperature is increased, there be (more / less) CO and H2 as a result.
18. Going back to the generalized equation in #15, if the temperature is decreased, then the reaction
which produces heat is increased, in this case, the forward reaction, producing more
(A and B / C and D).
19. 2 SO2 + O2  2 SO3 + heat
If the temperature is decreased on the above system, which reaction increases, (forward / reverse)?
There will be (more / less) SO3.
20. 2CO2 + heat  2 CO + O2
If the temperature is decreased on the above system, which reaction is increased? (forward / reverse)
There will be (more / less) CO2. There will be (more / less) CO and O2?
21. These examples have been illustrations of LeChatelier’s Principle which states that a system at
equilibrium, when subjected to stress, will temporarily adjust itself to relieve the stress. This means
that the shift to the right or left, or the increased forward or reverse reaction, will be temporary and a
new equilibrium will be reestablished.
22. Apply these principles in the following equations:
2SO2(g) + O2(g)  2SO3(g) + heat
What conditions of temperature and pressure favor high equilibrium concentrations of SO3?
(high / low) pressure; (high / low) temperature
23. 3 H2(g)
+
N2(g)  2 NH3(g) + heat
The commercial production of ammonia uses the Haber Process which is expressed by the above
equation. What condition of temperature and pressure will provide a maximum yield of NH3?
(high / low) pressure: (high / low) temperature
24. 4HCl(g) + O2(g)  2 H2O(g) + 2 Cl2(g) + heat
Increasing the temperature of the reaction will (increase / decrease) the forward reaction. Decreasing
the pressure on the system will (increase / decrease) the forward reaction.
LeChatelier’s Principle
Fill in all blanks with increase (↑), decrease (↓), or no change (NC). Under the SHIFT column show
LEFT (←) or RIGHT (→).
25.
N2(g)
+
3H2(g)
↔ 2NH3(g)
+
HEAT
Stress
[N2]
[H2]
Add N2
Increase
Pressure
Cool Rxn.
Remove NH3
Remove H2
Add Heat
Add H2
Remove N2
Add NH3
Decrease
Pressure
How can you make the maximum amount of NH3?
[NH3]
HEAT
SHIFT
Chart #2
Fill in all blanks with increase (↑), decrease (↓), or no change (NC). Under the SHIFT column show
LEFT (←) or RIGHT (→).
26.
H2(g)
Stress
[H2]
+
F2(g)
↔
[F2]
Add H2
Increase
Pressure
Cool Rxn.
Remove HF
Remove F2
Add Heat
Add F2
Remove H2
Add HF
Decrease
Pressure
How can you make the maximum amount of HF?
2HF(g)
[HF]
H = +541 KJ
HEAT
SHIFT
Directions: Indicate the effect of the stress on each substance in each reaction. Use the following
symbols to show changes in concentration and shifts: () Increase, () Decrease, (NC) No change, ()
Shift to the left, () Shift to the right.
27.
4NH3(g)
Stress
Add
O2
+
5O2(g)
[NH3]
4 NO(g) + 6 H2O(g)
[O2]
[NO]
 H = -906 kJ
[H2O]
Shift
Remove
NO
Remove
O2
Add
H 2O
Decrease
volume
Decrease
temperature
28.
C2H6(g)
Stress
Increase volume
Increase pressure
Remove
C2H6
Add
H2
Remove
C2H4
[C2H6]
H2(g)
+
[H2]
C2H4(g)
[C2H4]
Shift
29.
PbSO 4(s)
Stress
+
H+(aq)
Pb+2(aq) + 2HSO4-(aq)
[H+]
[PbSO4]
[Pb+2]
[HSO4-]
Shift
Heat
Shift
Add
PbSO4
Add
H+
Remove
Pb+2
Add
HSO4Remove
PbSO4
Remove
H+
Increase
pressure
30.
N2(g)
Stress
Add N2
[N2]
+ 3H2(g)
2NH3(g) +
[H2]
[NH3]
Heat
Increase
Pressure
Cool the Mix
Remove NH3
Remove H2
Add Heat
31. Given the equilibrium reaction, list 4 factors which favor a high equilibrium concentration of SO 3.
SO2(g) + ½ O2(g)
SO3(g) + 23 kcal
Explain how each of the following can affect the rate of a reaction.
32. The nature of the reactants means ___________________________________________________
This can make the reaction slower if ___________________________________________________
This can make the reaction rate faster if ________________________________________________
33. The temperature is equal to the ______________________________
Typically reactions proceed faster if they are ________ and proceed slower if they are ________,
because there will be more __________________ if particles are moving faster.
34. The concentration of reactants means _____________________________________________
If the concentration of one of the reactants is increased the rate of the reaction will _______________
If the concentration of one of the reactants is decreased the rate of the reaction will ______________
35. Increasing the surface area of reactants means ___________________________________________
If you increase the surface area of a reactant, the reaction will proceed _______________. If you
decrease the surface area of a reactant, the reaction will proceed _______________.
36. Catalysts ________________ the rate of a reaction without being _________________. This means
that catalysts are neither a __________________ nor a __________________.
37. List three ways to increase the rate at which a reactions proceeds:
_________________________________________________
_________________________________________________
_________________________________________________
38. If a reaction takes place very slowly, the bonds that are broken and reformed may be ___________
39. If you decrease the temperature of a reaction, the molecules will move __________________. This
causes the rate of the reaction to ___________________.
40. Which will react faster with water, a lump of calcium or finely powdered calcium? ______________
Explain: __________________________________________________________________________
41. A chemical reaction rate doubles when the concentration of one reactant is doubled. Explain this in
terms of the Collision Theory:________________________________________________________
_________________________________________________________________________________
42. Catalysts lower the energy of activation by ______________________________________________
_________________________________________________________________________________
43. Inhibitors slow down a reaction by ____________________________________________________
_________________________________________________________________________________
44. Using the Kinetic-Molecular Theory, give two reasons why reactions occur more rapidly at high
temperatures: ________________________________ ___________________________________
45. On the energy diagram below draw a curve representing the same reaction with a catalyst.
How do the activation energies differ? _________________________________________________
Does the addition of a catalyst change the final energy of the products? ___________
Explain__________________________________________________________________________
_
_________________________________________________________________________________
Visualizing Equilibrium
In the lab, Alejandro mixes two gases, A and B, inside a sealed bottle. He knows that A and B react
with each other to form substances A2B, and that A2B decomposes to form A and B. This reversible
reaction can be represented by the following balanced equation: 2A + B ↔ A2B
The pictures below show molecules of A, B and A2B per unit volume over a 20-minute period of
reacting. After examining these pictures, answer the questions below on Alejandro’s experiment.
46. In which of the pictures A-E is the system at equilibrium? ________ How can you tell?
______________________________________________________________________________
______________________________________________________________________________
47. How many molecules of each substance per unit volume are present at equilibrium?
A = _______ molecule(s)
B = _______ molecule(s) A2B = _______ molecule(s)
48. Predict how many molecules of A2B per unit volume Alejandro would measure at equilibrium if
he had started with half as much of substances A and B. ________
49. How would the reaction have proceeded if Alejandro had started with only A2B in the bottle?
______________________________________________________________________________
______________________________________________________________________________
The Reaction Process
Define each term below:
50.
Collision Theory: Theory that explains how molecules must ________________with proper
____________________ and with enough _____________ in order to react.
51.
Kinetic Energy: energy of ________________. This includes both ___________ and
_________________ (speed and direction.)
52.
Activation Energy: difference in energy from the ____________ of the diagram to the energy of
the __________________.
53.
Activated Complex: a _____________-lived complex formed during bond ________________
and _________________. It is neither _________________ nor ___________________.
54.
The Collision Theory states that __________________ must collide in order to react.
55.
A collision is effective if it leads to the formation of ________________.
56.
In an effective _________________, the particles must be oriented in a favorable position that
allows bonds to break and atoms to rearrange.
57.
Conservation of energy means that energy is __________________ from one form to another.
58.
The energy required to break bonds among reactants comes from the _______________
________________ (motion) of the reacting particles.
59. The difference between energy at the peak of the activation diagram and the energy of the reactants
is called the ____________________ ___________________.
60. When particles collide with energy equal to the activation energy, existing ___________ are
disrupted and new bonds form.
61. During the transition state, the reactants form an __________________ _______________ which is
short-lived and is neither reactant nor __________________.
62. The _________________ __________________ may then reform the original
__________________
or form new bonds and separate into ________________________.
63. The activated complex is a very short-lived molecular complex in which the _________ are in the
process of being broken and reformed.
64. Label the energy diagram to the right by
placing the terms reactants and products
in the appropriate locations. Indicate the
activation energy with a double headed
arrow. Place an “X” where the activated
complex is located.
How much activation energy is needed to
start this reaction? ____________
Is this reaction endo or exothermic?
_____________
65. The diagram below shows the oxidation of glucose as the forward reaction. For this reaction, the
activation energy hill is small. The reverse reaction, which is photosynthesis of glucose, has a
higher activation energy hill.
a. Which reaction requires a higher activation energy, photosynthesis or oxidation?
______________
b. Which reaction requires a net energy input, photosynthesis or oxidation?
____________________
c. Does activation energy have any effect of the net energy change of a reaction? _______ Explain.
______________________________________________________________________________
_
LeChatlier’s Principle
Directions: Match the change to the equilibrium system below with the letter of the appropriate
response. Each letter can be used once, more than once, or not at all.
2SO2(g) + O2(g) ↔ 2SO3(g)
_____ 66. O2 is added to the reaction.
A. The equilibrium shifts to the right.
_____ 67. SO3 is removed from the reaction.
B. The equilibrium shifts to the left.
_____ 68. SO3 is added to the reaction.
C. There is no change in the equilibrium position.
_____ 69. The pressure is increased.
Directions: If the statement is true, write “true.” If it is false, change the underlined word or words to make
the statement true. Write your answer on the line provided.
NH4Cl(s) + heat ↔ NH3(g) + HCl(g)
______________________ 70. The above reaction is exothermic.
______________________ 71. The production of ammonia from ammonium chloride will increase at a
higher temperature.
______________________ 72. As temperature decreases on the above reaction, more NH3 is formed.
______________________ 73. For the above reaction at equilibrium, an increase in pressure on the
system causes a decrease in the amount of gaseous ammonia.
74. What 4 factors affect whether a reaction at equilibrium “lies to the right or left” (favors making more
products or reactants)?
________________________________________
________________________________________
________________________________________
________________________________________
75. LeChatlier’s Principle states: “If a change is imposed on a system at _________________________, the
equilibrium position will _______________ in the direction that tends to ______________________ the
effect of that change.”
76. If more reactant is added to a system at equilibrium, the reaction will shift to the_______________ and
produce more _________________.
77. If a reactant is removed from a system at equilibrium, the reaction will shift to the ______________ and
produce more_________________.
78. Study the following reaction at equilibrium: 2NO2(g) ↔ N2O4(g)
If you increase pressure which way
will the reaction proceed? ____________ Why? ___________________________________________
79. How is LeChatlier’s principle used in the chemical industry? __________________________________
___________________________________________________________________________________
___________________________________________________________________________________
80. You are asked to produce HI from H2 and I2. This is an endothermic process. Write the balanced
equilibrium reaction for these gases and include the heat term on the proper side.
______________________________________
List 4 ways to increase the amount of HI produced:
_____________________________________
_____________________________________
_____________________________________
_____________________________________
81. Give an example of the use of the Haber process: ____________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
The Concept of Equilibrium
Part I: Matching
_____ 82. the formation of products from reactants
A. reversible reaction
_____ 83. a chemical reaction in which the products can generate
The original reactants
B. chemical equilibrium
_____ 84. the speed at which a reaction occurs
C. reverse reaction
_____ 85. the regeneration of reactants from products
D. reaction rate
_____ 86. the state in which the concentrations of reactants and
products remain constant with time
E. forward reaction
Part II: Short Answer
87. Explain how reaction rate and equilibrium are related. Give an example illustrating this relationship.
___________________________________________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
88. In performing most calculations with chemical reactions, it is assumed that the reactants are entirely
consumed. Is this assumption always appropriate? Explain.
____________________________________________________________________________________
____________________________________________________________________________________
89. Can all reversible reactions be observed in the laboratory? _______Why or why not?
____________________________________________________________________________________
____________________________________________________________________________________
90. Write the forward reaction and the reverse reactions for the following:
_____________________________________
2SO2 + O2 ↔ 2SO3
__________________________________________
91. List four factors that control the rate of a reaction:
1. _________________________________________
2. _________________________________________
3. _________________________________________
4. _________________________________________
92. The higher the concentration of reactants, the ( slower / faster ) the rate of the reaction.
The lower the concentration of reactants, the ( slower / faster ) the rate of the reaction.
93. When placed in a sealed container, N2 and H2 react according to the following equation: N2 + 3H2 ↔
2NH3 Over time, the rate of the forward reaction ( increases / decreases ) and the rate of the reverse
reaction ( increases / decreases .) During the course of the reaction the concentration of the reactant (
increases / decreases ), while the concentration of the product ( increases / decreases .)
94. Why will any chemical reaction reach equilibrium in a closed container?
_______________________________________________________________________________
95. Does a reaction stop once it has reached equilibrium? ________ Explain:
____________________________________________________________________________________
____________________________________________________________________________________
96. What is in the reaction vessel at time = 0 minutes?
97. Write the forward reaction:
98. What kind of reaction is the forward reaction? What happens to the RATE of the forward over time?
99. Write the reverse reaction:
100.
What kind of reaction is the reverse reaction? What happens to the RATE of the reverse
over time?
101.
Over time the concentration of which substance(s) decreases?
102.
Over time the concentration of which substance(s) increases?
103.
At what time is equilibrium reached? ______ Mark on the graph with a dashed line at this
point.
104.
At equilibrium which substance(s) is(are) present in the greater concentration?
105.
Is the forward or reverse reaction favored?
106.
What is in the reaction vessel at time = 0 minutes?
107.
Write the forward reaction:
108.
What kind of reaction is the forward reaction? What happens to the RATE of the forward
over time?
109.
Write the reverse reaction:
110.
What kind of reaction is the reverse reaction? What happens to the RATE of the reverse
over time?
111.
Over time the concentration of which substance(s) decreases?
112.
Over time the concentration of which substance(s) increases?
113.
At what time is equilibrium reached? ______ Mark on the graph with a dashed line at this
point.
114.
At equilibrium which substance(s) is(are) present in the greater concentration?
115.
Is the forward or reverse reaction favored?