Quick Reference for Chapter 15
Equilibrium- Constant
Expression (Kc)
Equilibrium- Constant
Expression –(Kp)
Relating Kc and Kp
Reaction Quotient ( Q )
K larger than 1
K smaller than 1
K larger than Q ( K > Q)
K smaller than Q ( K < Q)
Notes:
15.1 The Concept of Equilibrium
1) At equilibrium, _____________________________________________________________.
2) The relationship between the rate constants for the forward and reverse reactions and the
equilibrium constant for the process is
= _______________________________________.
3) At equilibrium, the concentration of reactants and products no longer change with _________.
4) For equilibrium to occur, neither reactants nor products can___________________ from the
system.
5) At equilibrium, a particular ratio of concentration terms ____________________ a constant.
____________________________________________________________________________
15.2 The Equilibrium Constant
1) The equilibrium-constant expression depends on the ____________________ of the reaction.
2) Write the equilibrium constant expression COCl2 (g)
CO (g) + Cl2 (g)
3) Write the equilibrium constant expression C6H12O6 (s) + 6O2 (g)
6CO2 (g) + 6H2O (l)
4) Write the equation to relate Kc and Kp
______________________________________________________________________________
15.3 Interpreting and Working with Equilibrium Constants
1) The equilibrium constant for the gas phase reaction
N2 (g) + 3H2 (g)
2NH3 (g)
is Keq = 4.34 x 10-3 at 300 °C. At equilibrium, ________________ predominates.
2) The equilibrium constant of a reaction in the reverse direction is the _______________ of the
equilibrium constant of the reaction in the forward direction.
3) The equilibrium constant of a reaction that has been multiplied by a number is the
equilibrium constant _______________ to a ________________ equal to that number.
4) The equilibrium constant for a net reaction made up of two or more steps is the
15.5 Calculating Equilibrium Constants
If we know the equilibrium concentration of at least one species, we can generally use the
stoichiometry of the reaction to deduce the equilibrium concentrations of the others.
The following steps outline the procedure we use to do this:
1) Tabulate all the known and initial and equilibrium concentrations of the species that appear in
the equilibrium- constant expression.
2) For those species for which both the initial and equilibrium concentrations are known,
calculate the change in concentration that occurs ad the system reaches equilibrium.
3) Use the stoichiometry of the reaction ( that is, use the coefficients in the balanced chemical
equations) to calculate the changes in concentration for all the other species in the equilibrium.
4) From the initial concentrations and the changes in concentration, calculate the equilibrium
concentrations. These are then used to evaluate the equilibrium constant.
______________________________________________________________________________
15.6 Applications of Equilibrium Constants
The equilibrium constant also allows us to 1) _________________________________________
______________________________________________________________________________
2) ___________________________________________________________________________
_____________________________________________________________________________
Reaction Quotient (Q) ___________________________________________________________
______________________________________________________________________________
Q=K _________________________________________________________________________
______________________________________________________________________________
Q > K ________________________________________________________________________
______________________________________________________________________________
Q < K ________________________________________________________________________
15.7 Le Châtelier’s Principle:
______________________________________________________________________________
______________________________________________________________________________
_____________________________________________________________________________
THE EQUILIBRIUM WILL SHIFT TO _______ WHEN:
MORE REACTANT IS ADDED ______________________________
MORE PRODUCT IS ADDED_______________________________
DECREASING OR REMOVING AN REACTANT ________________________________
DECREASING OR REMOVING A PRODUCT__________________________________
DECREASING THE VOLUME OF THE CONTAINER_______________________________
INCREASING THE VOLUME OF THE CONTAINER_______________________________
DECREASING THE VOLUME OF A REACTANT_________________________________
INCREASING THE VOLUME OF A REACTANT_________________________________
DECREASING THE VOLUME OF A PRODUCT_________________________________
INCREASING THE VOLUME OF A PRODUCT_________________________________
DECREASING THE PRESSURE______________________________
INCREASING THE PRESSURE______________________________
ENDOTHERMIC REACTIONS: HEAT IS A ____________________________
INCREASING THE TEMPERTAURE____________________
DECREASING THE TEMPERTAURE___________________
EXOTHERMIC REACTIONS: HEAT IS A _______________________________
INCREASING THE TEMPERTAURE____________________
DECREASING THE TEMPERATURE___________________
CHAPTER 14 AND 15 PRACTICE PROBLEM SET 1
1. At equilibrium, __________.
A) all chemical reactions have ceased
B) the rates of the forward and reverse reactions are equal
C) the rate constants of the forward and reverse reactions are equal
D) the value of the equilibrium constant is 1
E) the limiting reagent has been consumed
2. A reaction was found to be second order in carbon monoxide concentration. The rate of the
reaction__________ if the [CO] is doubled, with everything else kept the same.
A. doubles
B. remains unchanged
C. triples
D. increases by a factor of 4
E. is reduced by a factor of 2
3. Which one of the following will change the value of an equilibrium constant?
A) changing temperature
B) adding other substances that do not react with any of the species involved in the equilibrium
C) varying the initial concentrations of reactants
D) varying the initial concentrations of products
E) changing the volume of the reaction vessel
4. One difference between first- and second-order reactions is that __________.
A. the half-life of a first-order reaction does not depend on [A]0; the half-life of a second-order
reaction does depend on [A]0
B. the rate of both first-order and second-order reactions do not depend on reactant
concentrations
C. the rate of a first-order reaction depends on reactant concentrations; the rate of a second-order
reaction
does not depend on reactant concentrations
D. a first-order reaction can be catalyzed; a second-order reaction cannot be catalyzed
E. None of the above are true
5. The equilibrium-constant expression depends on the __________ of the reaction.
A) stoichiometry
B) mechanism
C) stoichiometry and mechanism
D) the quantities of reactants and products initially present
E) temperature
6. The reaction below is exothermic: 2SO2 (g)  O 2 (g) ‡ˆ ˆ †ˆ 2SO3 (g)
Le Chatelier's Principle predicts that __________ will result in an increase in the number of
moles of SO3 (g) in the reaction container.
A) increasing the pressure
B) decreasing the pressure
C) increasing the temperature
D) removing some oxygen
E) increasing the volume of the container
7. For the endothermic reaction
CaCO3 (s) ‡ˆ ˆ †ˆ CaO (s)  CO 2 (g)
Le Chatelier's principle predicts that __________ will result in an increase in the number of
moles of CO 2 .
A) increasing the temperature
B) decreasing the temperature
C) increasing the pressure
D) removing some of the CaCO 3 (s)
E) none of the above
8. In which of the following reactions would increasing pressure at constant temperature not
change the concentrations of reactants and products, based on Le Chatelier's principle?
A) N 2 (g)  3H 2 (g) ‡ˆ ˆ †ˆ 2NH 3 (g)
B) N 2O4 (g) ‡ˆ ˆ †ˆ 2NO 2 (g)
C) N 2 (g)  2O 2 (g) ‡ˆ ˆ †ˆ 2NO 2 (g)
D) 2N 2 (g)  O 2 (g) ‡ˆ ˆ †ˆ 2N 2 O(g)
E) N 2 (g)  O 2 (g) ‡ˆ ˆ †ˆ 2NO(g)
9. Which substance in the reaction below either appears or disappears the fastest?
4NH3 + 7O2 4NO2 + 6H2O
A. NH3
B. O2
C. NO2
D. H2O
E. The rates of appearance/disappearance are the same for all of these.
10. The value of K eq for the equilibrium H 2 (g)  I 2 (g) ‡ˆ ˆ †ˆ 2 HI (g)
is 794 at 25 °C. At this temperature, what is the value of K eq for the equilibrium below?
A) 1588
B) 28
HI (g) ‡ˆ ˆ †ˆ 1/ 2H 2 (g)  1/ 2I 2 (g)
C) 397
D) 0.035
E) 0.0013
11. At elevated temperatures, dinitrogen pentoxide
decomposes to nitrogen dioxide and oxygen: 2N2O5(g) 4NO2 (g) + O2 (g)
When the rate of formation of NO2 is 5.5 10-4 M/s, the rate of decomposition of is __________
M/s.
A. 2.2 10-3 B. 1.4 10-4 C. 10.1 10-4
D. 2.8 10-4
E. 5.5 10-4
12. Consider the following chemical reaction: H 2 (g)  I 2 (g) ‡ˆ ˆ †ˆ 2 HI (g)
At equilibrium in a particular experiment, the concentrations of H 2 , I 2 , and HI were 0.15M
0.033M and 0.55M respectively. The value of K eq for this reaction is __________.
A) 23
B) 111
C) 9.0  103 D) 6.1
E) 61
13. The data in the table below were obtained for the reaction:
2 ClO2 (aq) + 2 OH- (aq) → ClO3- (aq) + ClO2-(aq) + H2O
Exp. Number
[ClO2]
[OH-]
Initial Rate M/s
1
0.060
0.030
0.0248
2
0.020
0.030
0.00276
3
0.020
0.090
0.00828
A) What is the order of the reaction with respect to ClO2?
B) What is the order of the reaction with respect to OH-?
14. At elevated temperatures, molecular hydrogen and molecular bromine react to partially form
hydrogen bromide:
H 2 (g)  Br 2 (g) ‡ˆ ˆ †ˆ 2HBr (g)
A mixture of 0.682 mol of H 2 and 0.440 mol of Br2 is combined in a reaction vessel with a
volume of 2.00 L. At equilibrium at 700 K, there are 0.566 mol of H 2 present. At equilibrium,
there are __________ mol of Br2 present in the reaction vessel.
A) 0.000 B) 0.440 C) 0.566 D) 0.232 E) 0.324
15. The half-life of a first-order reaction is 13 min. If the initial concentration of reactant is 0.085 M, it
takes __________ min for it to decrease to 0.055 M.
A) 11
B) 8.2
C) 3.6
D) 8.4
E) 0.048
16. ) In the coal-gasification process, carbon monoxide is converted to carbon dioxide via the
following reaction: CO (g)  H 2 O (g) ‡ˆ ˆ †ˆ CO 2 (g)  H 2 (g)
In an experiment, 0.35 mol of CO and 0.40 mol of H 2 O were placed in a 1.00-L reaction vessel.
At equilibrium, there were 0.19 mol of CO remaining. K eq at the temperature of the experiment
is __________.
A) 5.47
B) 0.75 C) 1.78
D) 0.56
E) 1.0
17) The decomposition of NOBr is second-order with respect to NOBr and second-order overall.
If the initial concentration of NOBr is 0.102 M and the rate constant is 25 M-1 min-1, what is
[NOBr] after 1.0 min?
18) The first-order rate constant for the decomposition of N2O5 to NO2 and O2 at 70°C is 6.82 x
10-3 s-1. Suppose we start with 0.300 mol of N2O5(g) in a 0.500-L container. How many moles of
N2O5 will remain after 1.5 min?
19) The highly radioactive plutonium in nuclear waste undergoes first-order decay with a halflife of approximately 24,000 years. How many years must pass before the level of radioactivity
due to the plutonium falls to 1/128th (about 1%) of its original potency?
Problem Set 2
1) The equilibrium constant for the gas phase reaction N 2 (g)  3H 2 (g) ‡ˆ ˆ †ˆ 2NH 3 (g)
is Keq  4.34  103 at 300 °C. At equilibrium, __________.
A) products predominate
B) reactants predominate
C) roughly equal amounts of products and reactants are present
D) only products are present
E) only reactants are present
2) A reaction was found to be third order in A. Increasing the concentration of A by a factor of 3
will cause the reaction rate to __________.
A) increase by a factor of 27
B) decrease by a factor of the cube root of 3
C) increase by a factor of 9
D) remain constant
E) triple
3) Consider the following reaction at equilibrium:
2NH3 (g) ‡ˆ ˆ †ˆ N 2 (g)  3H 2 (g)
ΔH° = +92.4 kJ
Le Chatelier's principle predicts that adding N 2 (g) to the system at equilibrium will result in
__________.
A) a decrease in the concentration of NH 3 (g)
B) a decrease in the concentration of H 2 (g)
C) an increase in the value of the equilibrium constant
D) a lower partial pressure of N 2
E) removal of all of the H 2 (g)
4) Consider the following reaction at equilibrium: 2NH3 (g) ‡ˆ ˆ †ˆ N 2 (g)  3H 2 (g)
Le Chatelier's principle predicts that the moles of H 2 in the reaction container will increase with
__________.
A) some removal of NH 3 from the reaction vessel (V and T constant)
B) a decrease in the total pressure (T constant)
C) addition of some N 2 to the reaction vessel (V and T constant)
D) a decrease in the total volume of the reaction vessel (T constant)
E) an increase in total pressure by the addition of helium gas (V and T constant)
5)
Which energy difference in the energy profile
below corresponds to the activation energy for the forward reaction?
A) x
B) y C) x + y D) y – x E) x – y
6) The mechanism for formation of the product X is:
A + B  C + D (slow)
B + D  X (fast)
The intermediate reactant in the reaction is
__________.
a. A
b. B c. C d. D
e. X
7) Consider the following reaction at equilibrium:
2CO2 (g) ‡ˆ ˆ †ˆ 2CO (g)  O 2 (g)
ΔH° = -514 kJ
Le Chatelier's principle predicts that an increase in temperature will __________.
A) increase the partial pressure of O2 (g)
B) decrease the partial pressure of CO 2 (g)
C) decrease the value of the equilibrium constant
D) increase the value of the equilibrium constant
E) increase the partial pressure of CO
8) The rate law of the overall reaction A + B → C is rate = k[A]2. Which of the following will
not increase the rate of the reaction?
A) adding a catalyst for the reaction
B) increasing the concentration of reactant B
C) increasing the temperature of the reaction
D) increasing the concentration of reactant A
E) All of these will increase the rate.
9) The initial concentration of reactant in a first-order reaction is 0.27 M. The rate
constant for the reaction is 0.75 s-1. What is the concentration (mołL) of reactant after 1.5 s?
A) 1.7
B) 3.8
C) 8.8 × 10-2
D) 0.135
E) 2.0 × 10-2
10) ) Dinitrogen tetroxide partially decomposes according to the following equilibrium:
N 2 O 4 (g)  2NO 2 (g)
A 1.000-L flask is charged with 3.00  102 mol of N 2 O 4 . At equilibrium, 2.36  102 mol of
N 2 O 4 remains. K eq for this reaction is __________.
A) 0.723
B) 0.391
C) 0.212
D) 6.94  103
E) 1.92  104
11) A second-order reaction has a half-life of 18 s when the initial concentration of reactant is
0.71 M. The rate constant for this reaction is __________ M-1s-1.
A) 2.0 × 10-2 B) 7.8 × 10-2 C) 18 D) 3.8 × 10-2 E) 1.3
12) At 1000.0 K, the equilibrium constant for the reaction
2NO (g)  Br 2 (g) ‡ˆ ˆ †ˆ 2NOBr (g)
is Kp  0.013 . Calculate Kp for the reverse reaction,
A) 0.013 B) 1.6Κ  104
2NOBr (g) ‡ˆ ˆ †ˆ 2NO (g)  Br 2 (g)
.
C) 77 D) 0.99 E) 1.1
13) Given the following reaction at equilibrium, if K c  6.44 x 105 at 230.0 °C, K p =
__________.
2NO (g)  O 2 (g) ‡ˆ ˆ †ˆ 2NO 2 (g)
A) 3.67 x 102
B) 1.56 x 104
C) 6.44 x 105
D) 2.66 x 106
E) 2.67 x 107
14) If 60 grams of Acetic acid (HC2H3O2) and 60 grams of Ethanol (C2H5OH) are
allowed to react in a 1.00 Liter sealed container until equilibrium is established at 1250C,
how many moles of the Ester (CH3CO2C2H5) and water are formed and how many moles
of Acetic Acid and Ethanol remain?
Given
HC2H3O2 + C2H5OH _ _ CH3CO2C2H5 + H2O
Keq = 4.0
15. A particular first-order reaction has a rate constant of 1.35 × 102 s-1 at 25.0°C. What is the
magnitude of k at 95.0°C if Ea = 55.5 kJ/mol
A) 9.56 x 103
B)2.85 x 104 C) 576 D) 4.33 x 1087 E)1.36 X 102